Hi Gary,
Great question. The answer is, no, I don't believe that is a "known" quantity, because it would vary for each scenario, each search. How frequently one of your clients appears in the results is going to be based on a) it's strength, b) the strength and number of nearby competitors it has and c) the location of the searcher. So, as you can imagine, that varies, search by search, user by user.
A given in any scenario is that a business is only likely to rank for both truly local and remote searchers for the city in which it is physically located. So, let's say you have a dealership in Dallas. Someone in Dallas searches for "auto dealership" and your client has a good chance to rank for that. Someone in Sugar Land searches for "auto dealership Dallas", and, again, your client can rank for that. But, if someone in Sugar Land searches just for "auto dealership", Google is going to show him Sugar Land results, and your client won't be included in those because they are located in Dallas.
The variables in the scenario relate to the exact proximity of a user to your business at the time of search. A searcher in a Central Dallas neighborhood looks for "auto dealership" on his device, and Google is most likely to show him dealerships that are closest to him. If he then drives over to the Park Cities neighborhood and performs the same search, his results are likely to change to that geographic area of the city. But, if the searcher is, say, 10 miles outside of Dallas, searching for "auto dealerships Dallas", Google defaults to a different type of result for him, which appears to be based more on authority than proximity.
So, those are basically the elements that you have to take into consideration in trying to understand the reach of a given business. You have to consider the location of the searcher, as well as the level of competition both right next to the business, and within its entire city or zip code.
Not a simple answer, I know! But, I hope it helps.