Thanks for the ideas, everyone. I never thought those temps could be real.
I'll see if I can create a pocket for the stat probe between glass and mat without hurting the mat. If not, I'll look into finding a way to make a plastic pocket of sorts inside the tank for the probe.

Nagini won't be happy about having to be out in her holding tub while I mess with her home, but oh well

I'm off now to the R.M. expo to find a cute corn!