It's all about gun fit.
Have you patterned the shotgun?

1. take the shotgun and pattern it (most shotgun ranges have this) and figure out where it's really shooting for you. My guess is it's high or low.

2. Then, take it to a gunfitter. I've used Jim Jamison (he hangs out at Colorado clays usually, but others are avaialble)

Be some of the best money you spend.
I basically include the fitting in all new shotgun purchases (well, ok, not 870's, those I just shoot)