i have that problem with my 3 stack that i made but i think i know how to fix it this is my idea, since you use the ceramic holders like the ones at home depot right? im going to put a metal thing that will drop it down a little i forget what there called light box or something like that and then screw the cermaic thing to that so this will give it some air flow above the fixture and then what also i was going to do to mine is put a layer of foam between the cages so this will act as insulation i think this would make it work perfect the reason it heats up the next cage is because the cermaic thing is screwed right to the ceiling of the lower viv and that cermaic fixture gets hot which heats up the wood and so on and so on but i almost positive this system would work