In the end the group appears to need to be within a 4x4x4 to operate.
You can see that even though adding new generators is possible here, if they would extend outside of this space placement is not allowed:
Even though that last placement would not extend any row or column out past 4 generators, it would expand the placement overall to be 4x4x5 and that’s not allowed.
So for each stack of generators acting as a unit you’re allowed 64 positions for the 16 generators, as long as they are all connected on at least one side they will all act as a unified generator.