Appropriate Wheel Offset for 18" Wheels?

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Rear fenders relief cut and then pushed out a lot, I have 14 inches between fender lip and springs. 305/30/19 on 10.5 inch wheels fit perfectly, 1 inch from springs, 3/4 inch from lips...

When you mean "cut" did you cut/slice the outside wheel house that make the double wall on top of the rear fenders.

One my rear, the double wall make a step over that takes a bunch of room away. And there is that "thickness" of the fender even lower at the fender lip.

The step is pointed out with arrows here: