I suspect it's too hot...I'd take the hint since he's staying in the cool side. It doesn't much matter what the thermostat is "set to"...what actually matters is exactly
what the temperature is on the glass above the UTH, where the snake will make contact & can be injured when it's much over 90*.
Keep a couple things in mind: depending on the kind & depth of substrate, it's going to "insulate" the UTH, causing the heat to build up on the surface where the
snake will be hanging out...and even more so when it's also covered by a hide that helps keep the warmth from rising so easily. It's like if you're in a room with a
window open but running a heater, you're going to feel the heat, even though some does go out the window. You also want to be careful to make sure the UTH
was installed with a little "breathing room" so that the substrate (ie. "insulation") combined with a higher setting doesn't cause it to overheat & malfunction. If the
UTH doesn't provide adequate warmth in the enclosure when controlled to a level that is safe for the snake, then you might need to add an additional heat source,
or use a larger UTH (or maybe a second one for colder seasons, but always leaving at least a third of the floor unheated for safety.)
While you probably need to use a lower setting for the CHE also, I'd guess that your UTH is still TOO HOT, since you measured it by lifting the hide. I'd turn both
heat sources down....if you're using a CHE, set the UTH to 87-88* & see if that works better. You're lucky to have a BP that rejects the heated hide when it's too
warm, but don't rely on that...and anyway, you want him to be able to use the warmth he needs to function best...not linger in the cool hide if he needs to digest.