The setup looks absolutely beautiful; I'm sure you are so pleased to have it!
In these larger enclosures it can take a little time to get things dialed in. I am not familiar with Jungle Mix. I like coconut husk substrate, such as ReptiChip, that you add water to - stir in the water gradually and mix it around until the water is absorbed. You want the substrate to feel just slightly damp, but you don't want to be able to squeeze water out of it, if that makes sense.
You could also mix damp sphagnum moss into the substrate or (one of my favorite strategies) just provide a couple of big containers of sphagnum, and/or pile sphagnum up in a couple of spots so that the snake can choose microhabitats with more or less moisture.
Others will hopefully speak up if they disagree with me, but I don't see a problem with a cool side gradient of 75-80F, especially since your warm side is maintaining stable temperatures. So hopefully you don't need to continue suffocating yourself for the sake of your BP!