I'm always battling my snake's cool side's temperature! The warm side is fine, possibly even a tiny bit too high sometimes, but the cool side gets colder than it should. The UTH isn't too small because it covers a bit less than half of the cage. The ambient temp likes to stay on the low side too sometimes and it very annoying. I can't raise the UTHs heat though because then the warm side will be too hot! She has three hides, a large water bowl, and a rock outcrop thing that she climbs on. Her enclosure is a large sterilite tub. I can't remember the exact measurements but it is 38 gallons and very long. It isn't very tall at all and I use two layers of paper towels as substrate. I'm going to be switching her to a slightly larger glass tank soon and I don't want this issue with the glass either. I will be getting a bigger UTH for the glass tank though, don't worry. Any suggestions? As an example here are the temperatures I just recorded with my temp gun:
Warm side: 93 on the warmest spot
middle: 75
Cool side: 68 on the coolest spot