I had the same exact problem -- I was using two uth's. The warm and the cool side temps were fine, but my ambient was only at about 70 degrees. A che wasn't really an option for me (no place to install it in my custom wood enclosure). So, I went with a radiant heat panel from Reptile Basics.

I stopped using the uth on the cool side, and installed the heat panel to the ceiling on the cool side. I set the thermostat to 80 for the heat panel, and kept the warm side set at 92 -- voila! Temps are fine, and my ambient stays at 80.

I'd try setting yours up the same way, but with the che instead of a heat panel. I tried using the uth in conjunction with the heat panel, but it seemed like it was overkill, and the two didn't work very well together on the same thermostat. If I put the probe on the floor of the cage, then the heat panel never turned on, and if I raised the probe, then the uth would get too hot.

Sorry to be long winded, but I hope this makes sense, and help!

Just ask if you have more ?'s!

Later,

George