What you say doesn't sound too bad.

I too use a UTH to get my warm temp and a heat lamp over the cool side to get the ambient temperature. However... one thing I can say from somewhat hard-fought experience is that temperatures can vary over much shorter distances than you think. Its every easy to assume than there's a smooth temperature gradient because you have two good readings. With my setup I typically see the lowest temperatures *right outside the warm hide*.

* With your lowered room temperatures, I would definately measure the cage in several spots to see if you don't have cool spots which are likely the cause of drafts from the incoming fresh air and the cool glass surfaces.
* I would make sure to enclose the top as much as is safe. In my setup I have only one small sliver open over the cool side and about a 1/2 ring open around the heat lamp. Keep in mind that the heat lamp will drive a convection current so more air circulates than you might guess.
* I would seriously consider re-covering all three three sides of the cage with something more insulating. Trust me, this helps keep your ambient temperate even. I have had good results from rolled cork which can be obtained in a craft store.

Also, in my setup I have the "outside" probe from the accurite resting on top of the substrate right in the middle of the warm hide. Be sure to measure the temperature inside the hide as accurately as possible. The farther away your probe is the less likely it is that you have any real idea of what your snake is actually experiencing (which is what really matters!)




Good luck.