Tstat probe between glass and heater, or between glass and substrate..?

[Ashleigh91]

I am hoping to get my thermostat and UTH set up today, I've been using two low wattage heat lamps while waiting for my thermostat to get in ... anyway. I've heard that you have to put the t-stats probe between the glass and the UTH, but my UTH has already been put on the glass and the thing on the box said not to take it off the glass - I'm assuming that this can damage the UTH.

So my question is: does it really HAVE to go between the two, or can it be secured to the glass (inside the tank) under the substrate?

And I'm using the Hydrofarm thermostat, in case that matters.

Thanks.

Edit: And now I look down and see an almost identical thread that has already been answered.. feel free to ignore this... -.-