The XBF-1 should have a Floyd Rose and a locking nut, unless you’ve ordered a special without it (or bought a special offer with no locking nut). If so, the two plastic strips are probably to fill the gap where the locking nut went.

The ‘strip’ by the fretboard should then be a standard nut. You don’t want the strings in contact with the second strip behind that at all because of the additional friction.

If you are going the Floyd + locking tuners route, then the nut needs to be as friction free as possible. Standard kit plastic won’t cut it, but it all depends on just what’s fitted there as to what a good replacement would be.

So a photo is a necessity here to see what you have got.