With a 10" wide wheel, the +12 offset is just about perfect. It's positioned to the inside about as far as you can go without rubbing on the vertical upright (knuckle).
The outside, obviously, is another story. The tire will most definitely hit the outer fender if you don't have an adequate spring rate & ride height.
I'm currently running 750 lbs/in front springs, and 400 lbs/in rear springs, with a ride height clearance of 1.8" between the tire & fender. It just barely rubs at this height, so I plan to raise it slightly. Likely one turn of the coil-over collar.
Note that I run these in competition only. They're definitely overkill for the street.