Yep.
EG has a (had a?) technote on his website concerning advance/retard. His recommendation for max change is low..expressed in amount of movement, not º.
I'm leaving the actual number out to make YOU go find it...and read the whole thing, hopefully.
I don't run my bike on the middle mark, either. Spent most of an afternoon moving it here there, back and forth to get it where I wanted it.
A lot of flywheel pullin'.........
ha! I've got allen head screws on the rotor ring for the same reason they work good in the carb fuel bowl. Multiple removes makes the oem phillips heads a pain!