I am trying to set up a small Sterilite bin for my 100g BP. Note- he is still in his old enclosure while I try to get this right. I bought a 4" by 7" 4 watt UTH and taped it on with foil tape with the thermostat probe sandwiched right in the center. When I first put in substrate, it was still damp (eco earth) and maybe half an inch thick. After a couple hours with the lid on, I checked the hot side with a temp gun and it was only 70 and the humidity was 80. I bumped the thermostat as high as it goes, 108. I left the lid off a while to let the substrate dry, still too cool, humidity is 50 (but the water dish isn't in there yet), took out most of the substrate until it's only the tiniest layer, and I finally have it to 88-90 on the warm side. BUT it is such a small layer of substrate that it moves to the side and exposes the plastic bottom very easily, which reads at 100. I know this is too high. Do I set the thermostat to have the plastic bottom read 90 even though it will make the substrate cooler? Do I add more substrate, get a different UTH... ?? Help please!