I thought I understood UTH setup and was planning on following the diagram in the stickied post (1) where the probe goes between the enclosure bottom and the heat mat - but having looked at the instructions for the Ultratherm pad I'm confused...

(2) They suggest placing the heat mat on the underside of the enclosure with a piece of styrofoam placed underneath that to keep the whole mat in contact with the bottom of the enclosure. I thought you're supposed to have an air gap beneath the enclosure+mat? I understand why the styrofoam is being recommended since there's no adhesive to keep the middle of the mat in contact with the bottom, but is it safe to have it totally insulated underneath?

When I did some digging on the forum I also found a thread that suggested you can cut a probe slot in the styrofoam so it sits flush against the bottom of the heat mat, which I'm also a little confused about - does that mean the heat output underneath the mat is the same as above (vs sandwiching the probe between the mat and enclosure bottom)?

(3) Which then got me thinking about rack setups...how does is work to have the heat mat placed directly on the shelf/flat surface that the bins are being stored on work (again, no air gap)? BTW I'm not setting up a rack, just genuinely curious about how each of these scenarios work and their safety.

(4) Then after more searching, I found some recommendations to affix the heat mat to a surface (facing up) and leave an air gap between the mat and enclosure bottom. I mainly saw this on a UK site...doesn't really make sense to me.

I did some quick sketches with numbers to correlate to each option I was talking about to see if I understand them correctly (the little "sticks" on the ones with airgap represent whatever is used to elevate the enclosure, like furniture feet or what have you). Thoughts on each?