Hello and welcome to the forum and the wonderful world of snake keeping!!
Unfortunately, you're going to get lots of varied answers to most questions in the hobby.
But that's why it's important to cross reference multiple sources and learn from experienced, reputable keepers.
1) hot spot surface temps should be no higher than 90. I go 88-89. That is the temp on the actual surface of the enclosure. Snake's can and will burrow and push substrate around and lay directly on the surface.
These temps are found using a temp gun.
Ambient temps should be in the mid 80s
2) the thermostat probe goes OUTSIDE the enclosure. Sandwiched between the heat mat and the tub.
Leaving it inside it will be moved, peed on, laid on etc... which can all lead to inaccurate readings and potential heat spikes. These heat spikes can be dangerous and even fatal.
Your cool side should never drop below 75.
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