A thermostat probe and a thermometer probe go in two different places.

Thermostat probes should be on the outside of the enclosure right on the heating element.

Thermometer probe should go under the substrate right on the glass where the heating element is.

Some people use thicker substrates that can't be easily moved so it is more realistic for them to place the thermometer probe above the substrate. I use aspen and my bps move it around and get right on the plastic so I have to measure right on the plastic.