If you still have the FF string, it might be instructive to switch them back and forth in one shooting session to see if your observations are valid, i.e., a 1' difference in POI. Rather than change your gap to get them both to hit the bullseye, pick a single aiming point that will put both on the target and see what the spread really is.
Actually, people might be envious of you. People who mainly hunt are always looking for ways to reduce their gap at 20 yards. Maybe you've found a new way!