Ah yeah. No way i want to use a full size CHE in such a small cage. It's only an 18x18x18 cube. So i have the mini CHE in the back right corner of the cage so the rest of it as well as anything below the top perch where the probe is mounted will drop temps fast. The middle of the cage is around 79F and the floor of the cage is 77F.
I understand the concern but if you think about it, say the snake sits on the probe. The snake is say 79F which is the ambient of the middle level. Well the CHE would go to 100%. That would heat the air around the probe plus it would heat the snake. Once the temps on the snake hit 86F or the air around the probe hit 86F, it would shut it off. So really it doesnt matter if the snake sits on the probe or not since the snake is so small to begin with. I do agree, i would kind of worry if it was a full sized large CHE or a very thick heavy bodied snake. But really, if the snake's temp got too high for it, it would leave as long as cooler temps and spots were offered.
And yeah, i was kind of worried about the CHE size until i saw the Zoo Med Nano line of stuff. It's like a mini version made for their glass terrariums. Stuff works awesome. Like i said, the CHE is about 2 inches in diameter. They have a 25 watt version too which i tried but it wouldnt heat the perch past low 80s being on 100%. The fixture is only about 4 inches in diameter too which offers 3/4 or a little more of the cage to just be left with ambient room temp. They also offer red lights and basking lights for them as well in the 25 watt and 40 watt range.