Where do you put the thermostat probe?

So, I have a zoomed UTH on a jumpstart thermostat. The thermostat has a probe to regulate the heat, but I'm not sure where the probe should be placed. I've heard that it should be placed above the substrate where the snake lays. I've heard it should be burried under the substrate against the glass. And I've heard it should be placed outside of the enclosure right on the UTH itself. My question is, which one of these is best? I've personally had my probe under the hot hide just laying in there above the substrate. The thermostat always reads between 88-93. But the substrate never actually feels warm to me when I touch it. Is that because it needs to be burried? Also my snake tends to somehow move the probe out of his hide every now and then which messes up the temp regulating. This probe has caused me so much stress from trying to keep it in place, and figuring out where it needs to be. Please help.

I lay it right on top of the heat tape. In between the tape and the tub. I'll secure it with a little piece of tape.

I do what Cletus does, with one small hack...To simulate the plastic tub with heat tape below it, I have one empty space in my rack where a tub would be, I have a plastic tub lid laying on the heat tape and the probe taped to the plastic lid right above the heat tape area. This way I am simulating the temperature of the thin plastic tub right above the heat tape... just a tad more accurate than putting it directly on the heat tape itself.

I make radiant heat panels out of zoo med UTH's, mounted between two a piece of glass with the jumpstart probe between the pieces of glass (siliconed). I don't pay too much attention to the temperature reading, it will be off, so I use a laser temp gun to adjust the temperature precisely. If you put the probe where the snakes can move it or defecate on it, the reading can be thrown off and burn the snake. you can check out my photos to see more details of how I did it.