Help please! Problem with heat...

[Saml8]

We built an enclosure for our common boa (5' long 2' deep 30" high). We built it this high to give him a little climbing room but the heat panel I purchased is not pushing heat to the bottom of the cage. We purchased a pro heat 125 (125 watt). If I run it nonstop (never shutting off) I might be able to get the top of a black hide to around 88/89° but the inside of the hide which is where he likes to go after he's eaten a meal is not getting up past 80/82. The upper part of the cage is plenty warm…
I need a solution!!!

I thought about building a shelf about half way down so that I can put the heat panel under the shelf and make it lower to the bottom. Does anyone have insight as to whether or not this would be a good idea or any other solutions??!?

Thanks in advance