That 80 degree surface temp is something I struggled with. I found if I was going to get any kind of surface temp the first issue was way to much substrate. I was told 1-1/2 to 2” and no way would a UTH heat that up. I scaled it down and it’s approximately 1/2” now. I see 87-89 with thermostate set at 90. I get about 78-80 on cold side. Next was getting a good ambient temperature and found just heating under tank did nothing for ambient air temperature. I did not care for heat lamps and light cycle considerations so I use a thermostat regulated ceramic heat emitter set at 90 on hot side over UTH. On cold side I see air temps at snake height at 78 and 90 on hot. In center of tank it’s 84-85. I also covered 2/3 of tank to retain humidity. That I maintain at close to 50 percent or up. It was around 70 for the recent shed and it was a one piece shed.
My Pastel would not eat with a surface temp at 80. With the tank set as I explained above I have zero issues feeding and when it’s feeding day she is done eating quickly.
After many issues and some equipment failures this has been my success. I was also able to switch not only from live to F/T but mouse to rat all at once. I am basing this off of my snakes actions. She hides a lot but comes out and explores her environment usually at twilight. She when handled is very calm and shows no aggression and isn’t lethargic either. I have only been at snake keeping a very short period of time (6-7 weeks and have so much to learn but I really think if I were in your shoes I would get a secondary heat source. There are those with far more experience on here and I am curious what they have to say.