It sounds like your setup just needs some tweaking. First off...flexwatt performs best in our situation when the ambient room temperature is really high. For flexwatt to heat a glass cage hotspot as well as provide the proper ambient temps, the tape really has to work, creating a situation for burns if your snake contacted the tape indirectly through the bottom glass.

What to do? I don't really know for sure. You may want to look into heating the room to at least 78-80, and the heat tape will provide the proper basking temp without getting too hot to burn your snake.