Here is an example of why I don't put any of the hot-side stuff on top of the substrate in my set-ups. Note, my hides are the ones with bottoms on them. (Has pros and cons on that type of hide).

If you notice, my cold-side hide is on top of the substrate and the snake sometimes likes to go underneath it. If it was on the hot-side she could get too hot because my temp probe is under the substrate INSIDE the hide.

Just something to keep in mind.

Anyway, most hides don't come with a bottom, so your temp probe should be stuck to the glass under the substrate so that it is reading the hottest point of the tank that the snake can get to.

Check out my very pretty pastel curled under the hide.