stupid question about thermostat

I got my thermostat few days ago, I used to plug the UTH on timer, it works but takes a lot more work to tune the timer to suit the weather. So I tried setting up a thermostat, how do you guys put the probe? Do you lay it down horizontally or do you use the suction cup to stand it upright (with one point touching the substrate)?

I lay it down horizontally. I'm not sure what difference it would make, but I do get accurate temperature readings this way.

I concure with Olivia's method. I have mine lying horizontally right beside the hot spot on the tank. I have to set the temp a little lower than I want the temp but since I found the correct setting I have had zero troubles ith maintaining heat.

I actually put the probe on the tape itself. I feel it gives me a better reading of the thermometers in the cage. You will have to compensate for the thickness of the glass...
-Matt