ApathyAngel, it is clear you want what's best for Jeffrey and you have given this a lot of thought. That's great.
There has been great advice already, but I wanted to give my two cents and see if I can add anything useful.
Many Snakes, and I think BP's fall into this category, will choose safety (staying alive) over temperature (digesting food). Most of my snakes stay cool side or middle unless they are digesting or in shed. I offer identical hides for all my snakes on the hot and cool side and if there is room and the snake wants it (my BP and my corn snakes) I add a middle/ambient hide (sometimes a different size).
I would definitely try identical hides and make sure they are snug hides.
I like basic plastic hides (easy to clean and cheap). For example, https://www.reptilebasics.com/large-hide-box and https://www.reptilebasics.com/hide-boxes. Large or extra large are probably best. The only snake I use Jumbo for is my 6FT+ female boa who is almost 9 pounds/4+kg.
You can get them other places as well, but I they have a good description and suggestions for the different size hides.
Try offering the same size hides on the hot and cool side and see what happens. I think you will find Jeffrey likes it.