I just ordered a Cokin P adapter ring and holder off ebay. Atleast I'm assuming it's Cokin. I just got it today and tried to use it with my Singh-Ray NDgrad and it is super tight!! I'm actually worried I'll break the filter pushing it up and down the holder. Also my camera gets pushed up and down on the tripod. So my question is, is this common? Should I sand the filter down a little on the sides so it slides smoother? Or did I mess up by buying this cheap Cokin wanna-be off ebay and got a piece of junk, and should just go buy a Cokin one from B&H?