The magnet coverage is a factor in the motor's performance too.
I think I've read in various threads that is is best to have less than 100% coverage with the magnets on the inside of the housing, to have some gaps between them. Numbers in the 80% and up to 95% have been mentioned.
But I don't know where that difference would show up in the motors performance. I would guess it would be the RPM range. Or maybe it lets the ESC better sense the passing pole locations and deliver power more efficiently? Getting into some serious motor engineering considerations here now.