it is because your running metro flanges and have moved the wheels out 10mm each side so the steering arc is increased a little,
You maybe able to trim the leading edge of the wing/arch a little?
It isnt a major problem really but the sportspack minis had steering lock stops built into the rack to limit the lock so they didnt foul the arches or wings.
These maybe an idea if your very concerned????
Cheers
So if I drop an inch off the wheel width and run 10x5 with the same offset as my 10x6 GB it should give a bit better clearance? save cutting the wing?