I agree with Rick. Gills can get "nippy" and hard to catch on the surface. When this happens I add a dropper to the popper and hookups increase. It is weird because the gills are totally unpredictable if they are in the nippy mode or the actual "bite hard" mode. Don't over-analyze your technique. If the gills really want the fly, they will do more then just nip at it.
caribe