Front Rubbing - Tires, Suspension or Wheels?

Based on my measurements, the mounting surface of the wheel is roughly centered in the wheel well. I can only get a 18" TTII in an 8" width (or I can jump up to a 9.5"). If I understand this correctly, since my mounting position is centered, then I would want my bs to be half the width of the wheel. So for the 18x8 there is a 4.25" bs (with a -6 mm offset), so wouldn't that put me right where I need to be?

If I'm totally off then fine, but I tend to understand things better when I try to figure something out and then someone explains to me why I'm wrong as opposed to just telling me what I need.