And why would you do that, if I may ask? Is heat tape the superior heating device? You do understand that heat tape isn't the only way to warm an enclosure, right? And you do know (by Googling, of course) that the Habistat Vivarium Heat Mats are pretty much the same as FlexWatt? Im just saying.
Forgot to answer the question. It bothered (and still bothers) me too, you just have to accept that the temp will always vary from level to level. Best way to go about it is moving the thermostat probe around from level to level starting out from the middle and working down until you get a temp gradient that youre comfortable with.