Thamor,
The way for Japan to deal with a Sinkiang Stack is to flank it.
That multi-national force of FIGS there is great for defense, but can’t attack together. So Japan sends some forces to China (no real defense needed, just increasing from their 4-5 INF already in China in prep for later attack). But most of their forces go the northern prong (bury to Yak to Novo) or the southern prong (India to Persia to Kaz).
Upon reaching those points, the Sinkiang forces are flanked and the AF pulls out or risks loss.
THEN I take Sinkiang with the China forces.
Also, Russia FIGS in Sinkiang is a BAD idea for Russia. For those FIGS to attack and return to Sinkiang, they have to be attacking German forces in Caucuses (or Russia…). Otherwise, any use of Russian FIGS that started in Sinkiang leaves them elsewhere, and no longer an issue for Japan that round…
US FIGS have to GET there… a rather time consuming matter. UK’s have to get there also, but happens a bit quicker.
Eitherway, if Japan decides to focus on their Central Asia prong, they can hit Sinkiang with 4-5 INF plus 4-5 FIGS plus a Bomber on J2.