The B12's 5th is actually taller than the B6's 6th - and the sprocket gearing is taller on the 12. As far as getting 32 after your rejet, that sucks! I have to try HARD to get worse than 38 with mine. I think 36 is the absolute worst I've ever gotten with my Holeshot Stage II & slip-on.
If it's any consolation, I've tried to shift my B12 into 6th on more than one occasion - almost every time I've taken it out for a spin.