I think putting a mister in a ball python enclosure is over kill. Those are meant for amphibians and reptiles that require high humidity.

I would get some aluminum tape and cover 75% of the screen top with it.

Also, I don't think a 25g tall is very practical for a ball python. You are better off with a 20g long.

Why don't you just keep the snake in a tub if you are having issues with humidity?