You're right, under tank heaters won't really work. I'm only using overhead heat - the radiant heat panel. I have a hide below it, which usually stays in the mid to high 80s, and a couple of hides away from it which stay cooler (75-80F generally). Some flat pieces of stone beneath the panel near the entrance of her warm hide heat up to about 90F, so she has a slightly warmer basking spot if she needs it. It seems to work just fine for her.