Space or No Space

assuming you are using a racking system for you collection , do you prefer to use an air gap over the UTH/FW ? if so how much ?

reason I ask is that I have seen loads with ( like mine ) and a good few that sit just on top of the UTH/FW.

TIA

I like mine to be right on the bottom of the tub. I get better heat transferal that way.

I have a HerpEnclosure's rack, which has recessed heat. My free standing tubs do not have space.