As the title says the temps in my (homemade) rack are a bit off and it bothers me a little. It's a BP rack built of plywood and it's 12 levels high.

This is what I use:

CB70 tubs from Visionproducts.
A Habistat thermostat.
Habistat Vivarium heat mats.

The thermostat probe is placed on the third level counting from the bottom, it was placed on the sixth before but I moved it to the third to see if that would solve the problem.

The problem:

The temps are more off the higher I go in the rack. In the bottom I can have 89-90 at the hotspot (measured with a Sentry tempgun) and at the higher levels it can be 95+ and sometimes more. Some of the differance is caused by the snake as I use a bedding similar to Aspen, some snakes burrow down to the plastic where it naturally is warmer and some leave it alone and get's the desired temperature. But still the differance (wich is in my opinion too big) is pretty big and I've tried everything I can think of.

Anyone got some bright ideas for me?

Thanks