Just saw your latest post. The probe for my heating pad is sandwiched between the heating pad and the bottom of the tank. The probe for my CHE is suction cupped to the side of the tank about 2 inches above the substrate directly beneath the hotspot.

I have my thermostat set to 84 degrees but that creates a hotspot of 88-90 below my CHE. Your results may vary so you just have to adjust the temp on the thermostat and verify the actual surface temp with a heat gun.

You can place the probe in several different places and probably get the same results. That’s just how I do it.