Thermostat probe placement; best placement?

[rothsauce]

Have a R-Zilla 500W thermostat, but unsure where to put the probe to gain the best reading.

It seems to vary; some place them on the side of the tank near a corner, or under the tank near the UTH, others under the substrate in the center of the tank. What are others experiences, and/or preference?
I do not currently have a thermometer that can read surface temperatures accurately, but will be getting one shortly. My setup has slate tiles as the flooring, with sand underneath to help even heat distribution and to even out the plates. Currently the probe is in the corner behind the little gecko's warm hide, and the tank size is a 10 gallon until he/she gets a bit bigger and will be moved to a 20 gallon.

Thanks for looking!

 

[indyana]

For my leopard gecko, I tape my probe to the floor right smack in the center of his heat pad under his hide. I use paper substrate though, might be more difficult with slate. Maybe someone else with tile can comment on how they hold their probe in place.