BMV's car is a sixxer that most likely came with different steering stops (or perhaps none at all). There has been a note in the wheel pages of the FRPP catalogs concerning steering stops since at least as far back as 2008.
BMV must have SVT/GT500 look-alike
wheels if they're 9"/10" staggered as he indicates. The official 2007 GT500 wheels were 18 x 9.5, in approximately +45 offset, and used at both the front and the rear.
And for BMV's benefit, there doesn't have to be any problems fitting 10" wide wheels up front as long as you're at least a little careful about the offset. Hell, if you go to the right vendor of Mustang wheels, and maybe do just a little work even 18x11's with 285/35's will fit up front without any rubbing at all (the tread is entirely under the fender as seen from the top, see picture below). Whether you like the appearance or not isn't the point; they do work so two whole inches narrower at 9" is nowhere near the limit up front.
'08 GT coupe, 5M, wheels, tires, pads, fluid, a few suspension mods . . . still almost stock height
'19 WRX, 6M (the "family sedan")
'01 Maxima 20AE, 5M (the spare and occasional winter driver)