Under tank heater ?

I have had my corns in 29gal high with top infrared heaters only and we keep our house at 67° in the winter.
So I thought I would try UTH without the top heaters and see how the vivs stay for temps.
It's working great except for my one Butter wonton stay off the heater. My other snakes move back and forth from the hit hide to the cool hide.
Today I got my Butter out to hold for a while and she felt hot to the touch. Her surface temperature was 87°.
I held her for about 15 minutes and put her back.
She stretched out for a few minutes and then went back in the hot hide.
Checked her temperature again and its 86°.
Should I consider putting some astroturf or something over the UTH? Or am I worried for nothing?
If it were a Ball Python this wouldn't concern me, but I'm new to corns. Only had them for 4 months.
Please advise.
Thanks; Pine