Bob, you know the dumb question is the one that is not asked.
You can't do a system like this and have the transformers right next to each other at different sizes. Consider poles with transformers that are feeding a span in each direction throughout your system. There would be three spans between each transformer (one span would have no customers off of it as it would be connecting the to buses together. Since each transformer would be feeding several homes, there would not be that much current flow between the buses. However there would be some and that would soften the sags and take care of some of the voltage drop. The problem though is not the size of the transformers as much as a difference in impedance but the distance apart takes care of that with the impedance of the bus.
Downtown, we will use about the same size and impedance transformers everywhere and with the secondary lengths, that is not a problem.
With all that, consider that I am telling you what I have picked up over 35 years with IPL. I have never worked the downtown network nor do we use any connections between our overhead secondaries.
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Charlie Eldridge, Indianapolis, Utility Power Guy