But the whole "belly heat aids digestion" is a rumor with nothing to back it up, can't find any proof of this (If anyone can prove me wrong, please do). as along as your temps are correct it doesn't matter you can use UTH, back heat or overhead heat.
I prefer flexwatt to heat lamp because you use less energy for the same heat. also the lights tend to suck humidity. if you just bought a house, you will save yourself money overtime using flexwatt over heatbulbs
reason your getting so cold is your using a glass tank, switch to a 5 dollar sterlite tub and it will hold heat alot better