50” X 100” is the standard 9’ pool table size.
It’s not just the size of the pockets, it’s the fact that they are rounded - you can’t play off a pocket facing like an American table. Historically you just couldn’t play a ball down the long rail with any regularity. More recently the Chinese players have learned that if you pound the OB down the rail you can compress the pocket nose and force the ball in.
The top Heyball players are great at cross side banks to deal with balls near the side pockets.