I didn't decide on 330 ml of for oil, myself. I merely followed the specification listed in the CSC maintenance tutorial for fork service.
http://www.cscmotorcycles.com/Articles.asp?ID=263
I also know from seven years of experience studying, and working with Chinese motorcycles, that the forks are almost invariably low on oil as configured at the factory.
However, I do understand if someone wants to keep the same amount of fork oil as received from the factory. Everyone is free to configure his motorcycle exactly as he wishes.
__________________
Spud
"Never argue with an idiot. He will drag you down to his level, and beat you with experience."
Mark Twain
2015 Zongshen ZS250GY-3 (RX3)
2006 Zongshen ZS200GY-2 (Sierra 200)
2005 Honda XR650L
2004 Honda CRF250X
1998 Kawasaki KDX220
Mods made to my Zongshen ZS200GY-2:
http://www.chinariders.net/showthread.php?t=6894