I believe that Google ranks your pages on the basis of what they deserve with minor modifications.  All of my sites have double listings where they are strong.  Some have triple or quadruple listings where they are outstanding on multiple facets of a topic.

There are no "tricks" to getting these.  You need content that answers the query, there can be multiple ways of answering the query, and your content needs to blow the competition out of the water.

The only safe move here is to create amazing content for both blogs - but why have 2 blogs? Why double your effort when you could be using all the content to prop up the main site?

Andy makes a very good point here.  If you have a good article about Brass Widgets on your website and you decide that you want to write a second Brass Widgets article to publish on another website, then you are going to publish a second article that will compete with you and take some of your traffic.

Even if the articles are slightly different or very different they will still be "competing" - either at the short tail keyword level or the long tail keyword level.   The result will be damaging to your traffic.  The amount of damage will be proportional to the strength difference of your domains and  the diversity of keywords in the articles.  If the second domain is a lot more powerful than your own domain you could lose almost all of your traffic to the second website.

I have a website that publishes only unique articles.  Some of those articles have been written by other people in my industry who have similar articles or entire websites about the topics that they gave me to publish.  I never asked any of these people to write an article for my website.  Every one of them came to me with an offer.  With content written by these other authors, my website frequently outranks their website for primary and secondary keyword of the industry.  They might have a website that is powerful for the topic, but I have a website that is authoritative in the industry.  It can be hard to predict who will win at different levels but my site now competes and brings in lots of traffic for topic areas where I have never written.

Publishing on your own site, as Andy suggests, builds the strength of your site and does not invite potentially strong competitors into your keyword space.   There are benefits of sharing articles.  You get exposure as an "expert" on another website, which might have amazing traffic that includes visitors who will seek you out to do business.  You can often get a link on those websites that  will send lots of traffic to your website.  The best situation for all is if you simply want to get your message out to as many people as possible, but if there are competitive concerns then you must weigh the value of a link with the value of the exposure and the risk of a very strong competitor moving permanently into your space.

It happens a lot.  People who make it happen once often make it happen many times.

There are no "tricks".  To get two pages listed on the first SERP you must have two pages competing for the same keyword that are strong enough to earn positions in the top ten.   Some people can get three pages on the first SERP.   It is great to get #1 with multiple listings and push the second place site down to position #3.

One thing that I know is that you often have two pages strong enough but google will filter one of them from the SERPs because they do like to have domain diversity.  This usually occurs on highly competitive SERPs.  The easiest SERPs to get two pages ranked are long tail SERPs where the competition is thinner.

If you move the content and redirect the pages then you get new pages into the SERPs and get the value of redirected links.

What you don't get are things like brand mentions, domain type-ins, navigational domain queries, visitor behavior, SERP CTR, and more.  The more mature the website the more valuable these other assets might be.  Some of these assets will evaporate with the move, some will be reset to zero and others might be inherited.

All you can hope for is to do what you can to conserve these things.

When I see Google calling things spam, I steer way around them.

Other people have business models that flirt with the limits for another increment of competitiveness.

So, your idea of "pretty natural" goes up against something that Google sees as manipulation of their product and exploitation of their searchers.  They can nuke websites with the touch of a button or by the passage of a robot.

I have not used press releases for fifteen years.

Google might consider it a "link scheme" - especially if the press release contains multiple links with keyword optimized anchor text.

You can read what Google has to say about link schemes here.

If I see a study, I'll post a link here.

Are there any case studies about this issue?

Just the one that I published above.  The conclusion is... be prepared to sacrifice 80% of your traffic if you hide your valuable content behind a preview.

I would be asking the UX people to furnish studies that hiding content produces better sales.

We have lots of people raving about the abundance of content on our site, the detailed product descriptions, how much help we give them to decide what to purchase.  All of this content is why we dominate the SERPs in our niche and that, in many people's eyes, is a sign of credibility.  Lots of people say... "we bought from you because your website is so helpful".   However, if we didn't have all of this content in the open these same people would have never even found us.

Nobody has to read this stuff.  I would rather land on a website and see my options than land on a website and assume that they was no information because I didn't notice that the links to open it were in faded microfont because the UX guys wanted things to be tidy.    I believe that it is a bigger sin to have fantastic content behind a clickthorugh than it is to put valuable information in the open and allow people to have the opportunity to read it.

Putting our content out in the open is what makes our reputation.

I sure am glad that I am the boss here.  I can make the decisions and be paid on the basis of my performance.  

It was similar to a Q&A.  There was a single sentence question and a paragraph of hidden answer.  This page had a LOT of questions and a tremendous amount of keywords in the hidden content.  Thousands of words.

The long tail traffic tanked.  Then, when we opened the content again the traffic took months to start coming back.  The main keywords held in the SERPs.  The longtail accounted for the 80% loss.

About two years ago I had collapsed content on some important pages.  Their longtail traffic went into a steady slide, but the head traffic held.   I attribute this to a sign that the collapsed content was discounted, removing it from, or lowering its ability to count in the rankings for long tail queries.

I expanded the page, making all content visible.  A few months later, longtail traffic started to slowly rise.  It took many months to climb back to previous levels.

After this, every word of my content is now in the open.

Every site has these types of visitors.   I am sure that many of them are nice people. 

What's the difference between these types of visitors and paying for a billboard along a highway where you advertise to random people passing buy?

Your website will be relevant for some of these visitors and if you get enough of them guaranteed that you will get some sales.

I don't think that the Pope would mind if these visitors were dropping into his site.  He still gets to show them his message.  

Check to see if there is a duplicate or near-duplicate of your content out there.  Take a unique string of text that is a 10 to 20 words long.   Search Google for it between quotes.  See if someone is republishing your content.   Try this a few times with different portions of your text.

So if a site gets three pages ranking on the first page, they're all going to go one-after-another in the search results?

Yes or No.

If Google decides to show all three pages they will all appear on the first page of the search results.  However, Google, in my opinion, has a domain diversity goal and does not show all of the pages from a single domain in many situations.  Those pages that are not shown go into what many people call the "supplemental results".   You can see the supplemental results if you search to the end of Google and find their words....

"In order to show you the most relevant results, we have omitted some entries very similar to the 140 already displayed.If you like, you can repeat the search with the omitted results included. "

So, it is possible for you to earn three positions on the first page of google and only get one or two.

These "double" and "triple" listings can be very valuable because they push your competitor down the page.  They are very difficult, almost impossible to get in extremely competitive SERPs.  However, they are much easier to get in less competitive niches and can be worth going after.  I go after them a lot.  If I have a retail page and an article about the products, I often get positions 1 and 2 from that combination.  If I have several extremely different articles about a topic, I frequently get 2 or 3, or even 4 pages at the top of Google.

To achieve these you need a site that is one of the strongest in its niche and a site that has a prolific author who can produce more than one page that will rank well for the keywords that you are targeting.  I don't think that keyword cannibalization is a bad word because I've made a lot of money from it.

These sites have multiple positions because they have multiple pages that are strong enough to earn the first page and one page that is strong enough to earn #1.

To get above them, you will have to displace them from the #1 position or use Adwords.

We would like to understand why.

I doubt that anyone outside of Google has a good answer for this.  For some reason, Google thinks that your page is better promoted to the searcher with the short title.

Sometimes I debate with myself if one of my articles should have a one word title such as "widgets".  But, I usually go with a longer (but still simple and easily read) title that I believe will elicit clicks.   I used to think that Google was stinking up my clever marketing when they shortened my title.  However, now I think that I am a 70-year-old white guy who has lived in rural places all of my life and I have no idea what would appeal to younger people in different parts of the world.  So, if Google wants to shorten my title tag the results will probably be good. 

Learn which of these posts pull traffic or are consumed by on-site visitors.  Find out which pull entry traffic that processes through the cart.  Make more similar posts.

After that you will be left with some duds.  These can be improved or deleted.

If you have any doubts about this.  Decide if you want to put the value of your content out there exposed to the changing whims of the search engines.

The upside is what?  An artsy appearance?

The downside could be lower rankings, lower traffic, lower sales.

Worth it?   Not for me.