I've really been having a heck of a time getting my temps & humidity correct for some time. I'll give you a run down of my set-up..

20L tank
2 UTH's on either side (10-20 gal size)
screen lid
humidity about 56ish
2 dimmer switches attached to UTH's. I've noticed alot of fluctuation in the temps on these, I use a digital thermometer with a probe attached directly to glass under about an 1in-1 1/2 of Reptibark substrate. The temp on either side can be anywhere from 98-102, but when I hit it with the temp gun, it's about 85-88 on top of the Reptibark. My ambient temp is way too low, sometimes around 70, but fluctuates as well. The room is not drafty at all & I keep a blanket over the tank. I bought a 100w ceramic heat emitter & I'm not sure exactly where I should place this. I plan on putting the heat emitter on a dimmer as well. I guess what I'm wondering is if both UTH's & the heat emitter will be too much? I'm confused as to why my temps are so haywire & exactly what temps I should have the UTH's at to ensure the correct temp permates through the substrate. Also, is belly heat better than overhead heat? i.e the heat emitter? Any help or suggestions would be greatly appreciated!