Flexwatt Heating Source Placement

Hi,
I'm building a new cage for my snakes and decided to go with Flexwatt as the heating source, but I'd like to get some info on where to put it. I've been looking at the pictures of other peoples snake set ups and noticed that a bunch of people have but the flexwatt tape on the side of the cage instead of on the bottom of the cages. I expect this would keep the inner temp stable however the snake would not come in contact with the Flexwatt unless it was climbing the wall. Do ya'll think this would be a better idea that putting the flexwatt on the bottom of the cage?