Take the doors off and if you have a fan angle it inside.
I find especially with visions UTH do a super job of keeping the gradient. RHPs really perform best with a vertical gradient rather than horizontal. It is a choice, I also have yet to fine a really safe probe placement that works well. I would NEVER suggest a probe be placed where an animal can get between the probe and heat source especially with a radiant source. Everything is a little more complex with RHP and short enclosures (I believe Jeff Washburn recommends the face of the panel be 15-22 inches away from the floor???). It adds effort for little to no gain you will figure it out it just is harder and more expensive than it needs to be.