well, with these cars there is a lot of "play" in things... For every person who it would fit perfectly, there are another 3-4 where it wouldn't.
I think they put that in there so that it will fit everyone's car... Since it's attached to the fenders on the ends... where your fenders are in relation to the rad. support will alter things...
(Sure the fenders don't have a full two inches of movement... more like 1, at the very most...)
Just make sure you cut in very small increments until you get to something you like... yeah, it might take two hours or so if you cut very slightly... but it's better than cutting too much.
'66 Mustang, 302, front chin spoiler, R-model valance, '67 style Shelby hood, custom trunk and console.