I dont really know the answer in this case, but something to keep in mind. Less backspacing keeps the tires off the frame or leaf springs (in a sammi) but actually make it worse in the wheel well area down by the rockers. It's a delicate balance.
This is kinda hard to understand. I did a drawing in CAD to prove it to someone a while back.
This is viewing it from the top.
Yellow: wheel mounting surface
White: represents the wheel well
Backspacing issues can be fun , I wish I'd never went to the 2" backs on these 8" rims on the Sami . With the 12.5" wide Swampers the arc that the wheel turns makes it pretty hard on the arms , and it's very hard to keep the axle placed correctly to miss the front bumper and the tub . Instead of a wheel turning on an axis it swings in a large arc making clearance issues even worse . Centered rims on a wider axle would work out better ....
I am not sure how much lift you are running but I ran 31x10.5 on 15x8's with 3.75" backspacing and still had to trim back the insides of the front fenders.. I ran a 3" Calmimi body lift and the old 2.5" Procomp suspension lift.