Need help tweaking heat for Ball

[Sylorna]

Hello!
We have a male ball that is approximately 8 months old. We recently moved him from a much too small PVC display case to a glass 30gal glass tank with a wire top.
We are using a heating cord under the aspen to heat the tank. He has 2 hides, a stick to climb on and water available at all times.
He ate his first meal in the tank, but has refused meals since then. We are not sure if he does not like where his tank is now; if the new feeders are too big; if the new feeders just don't smell right (he has always had feeders from the same guy...same stock, but it is no longer available); if he's just being a male ball during the winter; or if he is not warm enough.
I bought a digital thermometer last weekend and covered his lid with tinfoil, as I read on another site that it can keep the heat in better. It certainly keeps the humidity in better. I left the lid without tinfoil so he has some good airflow. If you put the thermometer right up to the aspen on the hot end it reads 94F. If you raise it slightly and take the temp of the air it reads 85-87F. The cool end reads 78F. I'm wondering if we should be looking at A) getting a dimmer switch for the cording so he doesn't accidentally burn...if we do, what temp should I aim for? and B) if we should get a low watt bulb to raise the ambient temp a little higher.
He is still currently using both of his hides regularly and with the exception of the last 2 nights he has been coming out and exploring nightly.

Thanks for your help!