Rack Heating?

Ok, so do you put the thermostat probe into the tub or directly on the heat source? So many racks that I see don't have thermometers on them so I was curious where you put the probe? I am worried that if it goes into the tub the snake may lay up against it or something and scew the reading for all the other snakes. But hom much heat is not transfered into the tubs? If you put the probe on the outside on the heat source what degree to you put it at in order to ensure the right temp on the hot side of your tubs? Thanks for any assistance!

Goes on the heat tape

For my belly heat I put it directly on the heat tape, for my rack with back heat I have it taped to the side of the top shelf a about an inch away from the heat tape. I'm having troubles keeping my back heat rack up to the temp I want it in the winter. During the summer I had no issues with the probe taped to the flexwatt.