You're making some solid progress!!
Just 2 things jump out to me...
1) you want to measure the actual surface temp for your hot spot, not the substrate. Like Bogertophis said, they can and will burrow, push substrate around, etc...
So you want to get the actual glass temp down to 88-89.
2) the thermostat probe goes OUTSIDE the enclosure, sandwiched between the glass and the UTH.
Tstat probes that are INSIDE can be moved (even glued), laid on, peed on, water spilled on, etc... which can all cause inaccurate readings. These inaccurate readings can cause dangerous heat spikes.
Other than that, nothing else I can see.
I think you're going to love the RHP. They're fantastic.