i wish i could offer you some input, but i have zero supercharger experience.
however, i would make a "guess" that pulley ratio would have something to do with that.
are you running 1:1 or a slight overdrive ratio ?
if the AFR was reasonable when the boost came in, i think i would be happy with that. provided it stayed in the proper range with no detonation when floored as well.
i'm trying to learn all i can about this, as i would like to use an 8-71 on an early 392 to put in my "eternal project", that 33 dodge humpback delivery.
Cab knows way more about this than i probably ever will.