Braided loops

I recently bought some braided loops which came with a plastic sleeve. The sleeve is supposed to slide over the loop (once the braid is threaded onto the fly line) to be glued over the butt end of the braid, as a kind of 'cap', I guess to stop the braid end fraying.

Anyway, this plastic sleeve is about 4-5 inches long and I'm pretty sure it's intended to be cut down first.

Can anyone tell me if this is the case and what size to cut it down to. There's so much talked about rigs which do/don't turn a fly well, that I want to get this about right.

Thanks for any help.
Mark