You should always measure the temps in the hottest spot your snake can be exposed to. So, that is where you want your thermostat probe.

Sure, your substrate might only be 92, but if your snake burrows like mine do, the bottom of the tank or tub might be 98 or more and long term exposure could cause a burn.

You can also place the thermostat probe directly on the heat source, which is what I do. It one less wire for my snakes to bump loose.

Gale