This depends too much on the specific grid topology to be generally true. For example, there is an underground transmission line that is one of the bottlenecks

This depends too much on the specific grid topology to be generally true. For example, there is an underground transmission line that is one of the bottlenecks for about 30,000 people in my part of Pittsburgh. It's not too uncommon to have summertime glitches or outages due to overload on that one circuit. Any generation installed on the consumer side of that line helps - and that's several km. There's a planned solar project on an old partially reclaimed slag heap that will add generation proximal to that line, for example. (It's land that is too polluted for just about any other use, which is a fantastic place to stick some utility scale solar while still staying within the boundary of the city.)