Thanks. Yeah, the temp gun readings are on the top of the substrate. We have our AC set to 78 so it won't kick on until then, I meant that room temp will be 76 at the lowest during the day/morning. I do have a towel on part of the lid, foil will work better?

I think the fluctuation was mainly because I had just set up the UTH and it takes several hours, according to the instructions, to get to the right temperature.