Re: P-Rail: recessed rail on bridge pickups?
The stock bobbin toppers on those are attached in a kind of screwy way, such that I can see misalignment being very possible.
They just kind of sit on top of the bobbins...the tops of which aren't level with each other (the rail coil is not as tall IIRC, but I could have that backwards). Mine sat at an angle (perhaps purposeful, to match Gibson neck angles). I think they are glued in place, IIRC (but it has been a while). I snapped mine off easily (on purpose), shimmed them with wood to level them, and installed open trim rings.
The good thing is that the the plastic cover is solely cosmetic. It isn't part of the bobbins. So if it is on there a bit wacky, it doesn't affect the way the pickup operates – just the way it looks.
I suggest that all with P Rails do what I did: Remove, and then shim/level, the bobbin topper, and install open trim rings. It makes them look like a million bucks, while they look retarded stock.