Ambient air temps are often misunderstood in the role in thermal regulation. Snakes have large lungs (lung in some cases) typically extending at least 1/3 to 1/2 of the total length of the animal. It occupies the anterior end which also hold heart, liver,and upper end of the stomach. The lower end is kidneys intestines and reproductive organs. even when on a warm surface cold are will chill the blood from the heart and cause a dropping of the core temps. The animal will react by staying on the heat to try to lift the core temps up and in some cases causing burns to the exterior belly to try to regulate the core temps.

The air temps should be warm but not too warm the inverse can also happen. Typically mid to high 70s low 80s is what I'd suggest 85 is the high side for ambient air temps and 74 low side. The other thing to remember is if you have a enclosure that has a gradient (not just a hot spot and cold spot) you will very likely have a micro climate in the hides and in various areas. The air temps in those cases often will vary as well.

Measuring my ambient air temps I currently have mid point center 80º, hot side hide height is 83º cool side hide height is 76º the coldest point is is the front hot side low at 75º. The hottest point is hot side hide interior at 84º

The coolest point may seem odd but look at it this way the enclosure is a very well insulated custom plastic sided with sliding glass doors. The UTH causes the air to warm and rise and forces cool room air to enter around the doors and through the cool side vent (low in the side) The glass cools off and stays cooler than the rest of the interior so it also causes a localized drop. Combined the coolest ambient air temps are just inside the glass door beside the vent. I am careful to place the hot hide at the back.

I hope this helps some.
Alex