Thanks for providing the background on what you are doing. In general retail stores have no capacity and thus the maximize market share does not try to limit that. Also, it is not working on "demand" to which one can apply the notion of capacity. What is is working on is the probability of a spatial interaction between the store and customer location based on distance away and the distance decay (power or exponential) that has been calibrated from some known behavioral analysis for the area and the product mix.
So the only thing that will limit the interactions is the impedance cutoff. e.g., Customers do not come from more than 10 Km away. Sorry there is no notion of capacity in this case.
As far as demand point being census group points, all I was suggesting before is you can take the same location and add it again but halve the number of people that are there. So the total amount of people at the location is the same except they are now split into two separate points that can be allocated separately if you use the max capacitated coverage solver.