The logic here is that if ambient temps dip lower than you expect in a cool room, belly heat will more efficiently heat the snake itself if the tub as a whole briefly dips below where it ought to be. back/side heat wont give the snake the same warm spot. Also, I've had great luck using large-ish but quite short hides that cover the majority of the hot sot that are capable of maintaining hot hides with appropriate ambient temps even when the temp in the tub isn't ideal. Its a backup for when things dont go as planned. you wouldnt be able to put a hide over top of a hot spot generated by tape on the side or back of the tub.