should i place the probe on top of the substrate or on the bottom of the cage? I am using shredded aspen as a substrate. 2nd question, how deep should the substrate be? I'm keeping a deppei deppei with an UTH on a rheostat. the temps on top of the substrate never go above 80f on the warm end but my temp gun shows the heat pad to be about 100f. the cage is raised 1 cm above the floor.