Of course a CHE changes the ambient temp. That is an overhead heat source pumping out a ton of heat. Sure it is a more directed beam than a flooding heat bulb but it has heat spill that reaches and warms the entire cage.
A UTH on the other hand is a under tank heat source that should only be putting off enough heat to get a nice hot spot of 88-90(on the cage floor). An UTH is not meant for heating the entire cage, though many people believe they are.
Comparing the effect of a CHE is nothing like a UTH.
Im just glad the OP didn't have the substrate so thick they had to have the UTH pumped up and caused a burn on the snake when it moved the substrate aside.