CHE, it needed?

i hear alot of people who say a UTH is better then the bulb since were dealing with snakes here and the belly heat is more important then from above. i have my probe on hot side inside hide mixed in with subtrate so i get the temp that she's getting.

Well, my BP usually chills on the cooler side most of the time. Should i switch my heat source from the bulb to the UTH? and if so, i have a 150w for my 20 gallon tank. What should i switch to for light?(watts) and the UTH goes on the warm side?

Mind you everything in my tank is fine, temps ( both sides ) and humidity, so is it nessecary to even change? or is this pretty much a must?