Another step to promoting bigger organisms to evolve is as suggested by tilsk in the Discord server to make cells radiate less if they have more connections. Essentially, this would mean that bigger organisms have longer lifespans than smaller ones (given that there is a base radiation set above 0 in a given zone), because they would lose energy at a much slower rate which is how it works in real life.

You could have a setting that controls the intensity of the discounted energy radiation. I would also suggest having it multiply if a cell with many connections is also connected to another cell with many connections so that the bigger the organism is, the more energy is stored in the center. Basically if two cells have 6 connections each, both of them would benefit from that more than if one cell with 6 connections was connected to a cell with only one, and it would accumulate if more cells are added to the equation.

I think it's worth trying out, but I also think issues such as #118 need to be addressed as well before this will have a noticeable effect.