[chairman]

I'm going to summarize your setup from your description, please correct any mistakes I make.

You have a thermostat controlling room temperature that is apparently set to 70F.

You are relying on the room's thermostat to keep your rheostat on the basking bulb accurate.

You have a thermostat controlling the temperature of the UTH.

To fix your temperature problem you could try:

Switching your bulb to a spot light, maybe even a lower wattage one; this will direct heat to the hot spot with less impact on the overall cage. (Flood lights and standard shaped bulbs direct heat differently than spot lights.)

Change the height of your bulb.

Move your bulb further to one side of the tank than the other.

Change the angle of your bulb, perhaps aim it at the hot side.

Get a thermostat for your heat bulb.