I just purchased my first Zeiss Conquest 3-9x40 and I ordered a set of Butler Creek flip open lens cover following the Butler Creek size chart of 14 eye and 25 lens. The 25 lens fits fine but the 14 eye is too small to fit over the fast adjust ring. What size BC flip open eye size works for you?

The best fit over the large rubber piece on the eyepiece is an EYE 19.

Sorry I can's offer specific advice in your situation and I'm glad Jon has done so.

My observations have been that:

You never have the two you need in the shop,

And no matter how you measure for a pair of them one is always wrong. Don't feel bad.