I use the flatter section on the rear on nylon or ABS plates, helps to sit flush. Depending on the snaps some can only go together one way as the stem length differs, many I've used don't though.
Domed on the elastic side
Only apply the glue to the nylon, not that it's happen to me but I have heard some have had issues with glue and certain snaps, can cause some heat when drying. Interesting thread here on the subject, another here
Make sure you rough the area of armor with some sandpaper to give the glue something to grip too.
Also once cut run a lighter or soldering iron across the cuts and melt to stop fraying, or even glue, nylon can fray quite a lot if not sealed.
Using some scrap pieces of ABS can help clamp and lay the nylon flat while gluing