capt. howdy, to the best of my knowledge the prob that you have on the hot side should be down on the ground semi burried in substrate so you can get a reading on the temp he's laying on.
the air temp could be 80 but he might be burrying into 100º substrate

and to welwood, you might try taking some substrate out? maybe your UTH is trying to heat up to much aspen so when it gets to ur temp gauges its way down