Re: scope covers
Gavin, I can't verify the NF 50mm Obj size, but can verify the 56 is correct. The fact that eyepiece changes power will always change the orientation of any cap on a NF. IMO, its best to orient the cap with the ranging power as that is the power I find myself using the most.
That being said, take a look at your cap. Lots of times guys trial fit these in the store only to put the cap in a package marked for a different size. Found this out the hard way when I took a NF 56mm scope in to buy caps. I had two NF 56mm scopes I needed caps for so I took one in to fit them. Found the ones that fitted bought two of each, came home, and one didn't fit my other scope. Found it it was not the right cap for the package.
Take a look at your BC Flip up. It is marked what size it is on the inside of the flip up. The guide may very well be messed up, I don't know. But off the top of my head, I don't remember anyone else saying this happened to them.