I just got my first BP last Friday and am positively besotted with him. He's friendly and, as of yesterday, eating well. I do have some specific concerns about his tank temperatures that I haven't been able to find answers to, though.

I have him in a Zilla 20L with two small, identical hides on either end and a larger hide plus some branches and leaves in the middle. He has a water bowl on the cooler side big enough to soak in. I'm currently using an overhead red heat lamp for warmth, which keeps the warm side in the mid-80s and the cooler side unfortunately in the 70s, usuall lower 70s. Despite this, he tends toward the cold-end hide.

I would like to switch him to an under tank heater so I can cover the screen top with foil to retain humidity and try to cut out the heat lamp as much as possible. I've read everywhere about temperature gradients and under tank heaters, but it all seems to be very general info. So, without further ado, my questions:

Does the high-80s temp apply to the glass directly over the UTH?
If so, what range should my ambient air temp range be? What about the temp of the substrate above the UTH?
Should I be concerned that he prefers the cold hide even though its cooler than advised? He only stays in the warm side for a short while before going back, but he is eating and shows no signs of lethargy or difficulty breathing.

I'm receiving an Accu-rite temp/humidity guage and a ReptiTemp 500R thermostat tomorrow for this and already own a 20gal under tank heating pad.

Sorry if I gave way too much info...like I said, I think I might be a bit overanxious.