80/90 is a great gradient with a boa, pretty much the standard I feel like. My Hog (which are known to prefer slightly cooler temps) has a cool side of 78 and loves it though.
I 100% agree with Richard though, and if you want to test out the theory.....take a shed from your female and put it in his cage. See if he responds, but I HIGHLY suspect he will. If that's the case you might have to move your female. The temps dropping this time of year along with the proximity to your female will trigger the mating response.