Hmmm, ... reminds me of a similar problem I ran into last year. I relocated my boas into a different part of the house away from the snake room. I just could not get the temps up on the cold side (didn't go any higher than 72 degree). Tried a separate heat mat, just to find out that it messed up my oh-so-perfect humidity settings <grrgh>. Ended up going to the hardware store just to see, if I could come up with an idea and ended up taking a roll of alumium insulation home, cut that to the same size of the bottom of the enclosure and - lo-and-behold - the aluminum distributed the heat all the way to the cool side of the tank and brought it up to 78 degree without any further adjustment.