Little late - i've got a giro Cinder in medium, and have just bought a pic ventral air, also medium.
Both fit comfortably, the POC perhaps slightly snugger. Only other thing I can think of: if you push the helmet forward from the back (ie reach behind and push the helmet forward), there are two hotspots right at the back of your head, but you can't feel them normally.
Edit - got the names wrong, i've got a girl cinder, not synthe
Little late - i've got a giro Cinder in medium, and have just bought a pic ventral air, also medium.
Both fit comfortably, the POC perhaps slightly snugger. Only other thing I can think of: if you push the helmet forward from the back (ie reach behind and push the helmet forward), there are two hotspots right at the back of your head, but you can't feel them normally.
Edit - got the names wrong, i've got a girl cinder, not synthe