Temperature settings on an UTH hooked up to a thermostat

[Mikoh4792]

As some of you may know, I have moved my Cay Caulker's boa into a setup with an UTH. The temperatures are good, however I have to set the thermostat to 101 F in order to get a 90F hotspot. I'm sure the hotspot is at 90F because I have checked it with multiple instruments. Two infrared heat guns, and two digital thermometers. There is only an inch layer of substrate(Mix of cochusk and cypress mulch).

Some of you have told me that you only need to set your thermostats a few degrees above your desired temperature. Why do you guys think I have to set mine so high? My room is always warm in the summer, currently it's 82F inside so I just turned on the AC to bring it back down to 75 so my snakes can have an actual cool side.

Cliffs just to keep it concise:
- Helix thermostat set to 101 just to get a 90F hotspot
- 1 inch layer of bedding(cocohusk+cypress mulch)
- It isn't the ambient temperature of the room, since the room is usually warm.