Not quite sure why you are quoting me and talking about the floor space. I give my adult boas the equivalent of a 6x3x1.5 which is plenty for an adult boa.
And honestly 45-50% humidity is NOT high enough. The lowest you want to go is 60% with optimum of 65-70%. Sure they can live in it but again, just like overfeeding(which im not going to get into again), you wont notice the damage until its done. Snakes from higher humidity regions need that humidity not only for hydration but also to keep their lung from drying out and cracking which can let bacteria in which causes URI.
And misting can compensate for the lack of humidity only so much. You dont want to make the snake sit in a constantly wet environment as that is breeding grounds for bacteria, fungus and mold which can lead to any number of RI be it fungal or bacterial.
You are right though that floor space is more important than height.
I do mist my cages though but usually only once or maybe twice a week in the winter and it completely dries out and keeps 65-70% humidity.
Another thing you can do OP is use a mister to help with humidity if you are set on that cage but you need to cover at least 3/4 of that top to control the air flow or else no matter how much misting you do, you wont beat the whole rooms humidity lol.