The point in having a cool side and a hot side is so the snake can have a heat gradient. Essentially, the snake needs a way to get away from the heat. If you have a UTH on the cool side, it is not a cool side anymore. My guess is the snake is too warm!!
When I had a glass enclosure and needed a low wattage heat lamp to keep up the ambients (I used a 50W red bulb day and night, on a 15 gal. aquarium - you can also use a straight up heat lamp with no light) I had the lamp kind of in the middle but slightly more to the warm side, where the UTH was.
You need to have a place where the snake can be free of heat sources (or rather, about 78-80F INCLUDING the vive floor). Too much heat makes for an upset snake...