AMBIENT temps and SURFACE temps.

Hi guys and gals, a little help required please. I keep my BPs in RUBS with kitchen roll on the rub floors and use UTH with thermostat.
For temperature readings I use both high quality digital probes for the ambient temps and infrared temp gun for the surface temps. I place the digital probes ON TOP of the kitchen roll for reading the AMBIENT temps, at the cool end I get a reading of 85°F and the warm end I get 90°F
For the SURFACE temp readings I use an infrared temp gun and take a reading from the kitchen roll surface and get the following readings.....cool end 81°F and warm end is 84°F. So firstly am I putting the probes in the right place, second are my temps good for surface and ambient range. Thanks in advance, Martin.

Pull up the paper towel, you won't get a good reading on the paper towel.

I'd be skeptical about that discrepancy. When in doubt, use the infrared reading in my opinion. If the plastic is clear it may not give an accurate reading directly, so I would actually disagree with the first post and say to check it on the paper but IMMEDIATELY after you pull it off the heat. The paper will drop very quickly once you slide the tub out. If your cool end is giving you over 83 I would lower the heat a bit.

Since it's belly heat the air is cooled way more then the floor temperature, and paper towel will always have air between it and the plastic. Air at 20C also has a heat conduction level of 0.023. When you hit the paper towel it'll be only slightly higher then the ambient air temperature, but when the animal presses down on the paper towel they get much more heat. Paper towel is under a quarter inch thick, there's very little heat loss between where the plastic is and the top of the substrate.

You want the actual temperature of the surface your snake can touch.
This would be under the paper towels.