If possible, could you please give some more details about what you see happening in China?
This as nothing to do with CHS.
It's true the AI is completly brain dead in China, having played the AI campaign 15 twice into mid-43, once as allies, then as Japan. It's far to easy to run amuck all over China. The AI does nothing in response to capture of key bases such as Hanoi and Haiphong. When playing the allies after taking Haiphong, I was able to move ships from Manila to Haiphong and use it a sub base and airbase with no response from the AI.
CHS - China, playing as allies, it's far to easy to move Chinese troops into Nanning, Pakhoi, then go into Hanoi, Haiphong, Hue, Ubon, Lang Prabang early in the game.
Maybe for play balance, Chinese troops outside of Nanning should start in Kunning, and Japanese troops be beefed up.
You almost have to create two scenarios with Witp, one for playing against the AI and one for playing against other players.