Friction zone is a niggling issue with the hydro clutches because there is no provision for adjusting it like there is on cable clutches. I guess I have just gotten used to where it is on my bike.
Bear in mind that as the clutch plates wear, more fluid will be displaced into the master cylinder, and it will become more full.
As Jerry said, the master cylinder should not be overfilled. If the master cylinder gets too full, the clutch can start slipping because it can't fully engage because of all the fluid pressure in the system. This would normally only really be a problem if the MC was almost totally full with very little air at the top, and after the clutch plates have worn significantly... but it can happen.
Ken