Not cut lapping, zipper cutting. To all you long time glassers :-) do you find zipper cutting is easier with poly? Have gone completely cured, close to completely cured, and further back, and the cloth doesn’t like to ‘crease’ at the edge of the tape. Cut lapping no problem (epoxy). Zipper cutting lifted lap edge. Am I simply not opening up enough before zipper cutting? More onto the straights before lifting the tape? Any doubts fresh blade :-).
You need to make short relief cuts at the nose and tail. Then cut those pieces away. One on each side of the nose. One on each side of the tail and across the tail. This will remove the glass and tape at nose and tail. Removing these pieces will make it easie to fold back the cloth and tape as you go. Also; removing these pieces will have to be done before the resin has completely set. It has to be done at gel stage or a little harder. The reason is that you will need to cut down into the glass to make these cuts. You can’t fold the cloth back with these pieces intact. So you have to cut downward to start the process. Then you can proceed to folding back and cutting along the edge of the tape and not downward and into foam.
I’m not a pro like McDing but do agree that if you can cut the relief cuts nose and tail just after gel then your zipper will move easier (bend outwards). I think the Shrednaught youtube channel has a handy tip of making a slight bend in the middle of the blade after your nose/tail relief cuts into the foam (so there’s a little subtle U-shape) to allow it to slide underneath the lap and with relief cuts in nose and tail and gentle pulling back of the lap you should have an easier time with zipper cuts. Did I misunderstand your Q?