When I first moved to my current home I installed a big wood stove in the basement to help keep the home warm. Over the next few years I learned a lot empirically about how fire works.

One of the more interesting lessons was how important it is to use the radiant heat from a burning piece of wood to build and sustain heat in other pieces of wood. It works a bit like fuel rods in a fission reaction. When you keep the logs separate they will burn, but not vigorously. But if you bring two glowing logs close together, you can see them mutually heat each other and drive up the rate of combustion.

I think something like that happens with these concentrated communities.