I found out the hard way that I needed some additional divisions in China, I was so overstretched in my first game that I ended up with single garrison bde holding the line. . .
Did you reorganize your inf from triangular to . . well, what do you call it? Biangular (2 inf bde per division)?
I reorganised my garrisons in the north to 2 bde Divs in order to simulate the need of garrisioning the border.
IIRC you just have to beat ComChi by strategic retreat and breakthrough, after that do a naval invasion at Shanghai and NatChi is screwed.
For almost the whole war I held the mountain border in the north against Xibei San Ma and parts of the border with NatChi with garrisons.
The only thing I question is this. will Japan benefit from it in a supply reason with 1.3? It was said supply could be traced from honeland that produced ICs. I Don't remember much ICs in Korea. If KOrea had some ICs, would it help supply the units in the China area?
Thats only to help against the exploit of just taking an enemy capital to shut down supplies for the army. It wouldn't work anyway since the supplies still don't travel through puppet territory.