When fitted properly, they do not interfere with the ball (they are very thin)

But I have seen them not fitted properly and left floating 5mm above the playfield

Yeah one of the ones (the one that was already there) on my BSD is like that, good 3mm above the playfield on the side the ball comes in.. going to have to re-install it.. most I have found use double sided tape on the non screwed down side to stop them lifting..