so you are saying the fag is bigger diameter and caused issues with whatever rotor you are using?
the hat wouldnt fit properly over it?
what kind of rotor is it?(the make)
how do you know the fag is actually bigger than what came on the car from bmw without actually comparing it to the bmw stamped piece(which was likely made by fag fyi)
this just sounds like some minor variance when fitting different aftermarket pieces together.(the issue could be the rotor hats themselves,the bearing or none at all. Maybe it was badluck and you got both on their outer tolerance limits) and since they are from different companies its possible there is some over lap with those limits.
I should measure my bearings to compare. As far as I know mine as still oem(and two need replacing)