It seems that as long as there seems to enough manpower to reinforce all troops at once up to 20% of all IC can be invested by the AI to reinforce. But never more than this value that is also saved within the savegames. Therefore it can be manually manipulated. Especially in case of China increasing this value helps a lot. In case of Germany this may help, too. But there may come a point of no return where the AI thinks there is no hope to reinforce its troops and does not even try. This of course increases the need for reinforcements more and due to decreasing fighting values of those poor units they suffer even greater losses and therefore the need for reininforcemets grows even further. It is a vicious circle.
My observations are still not completly conclusive. But somehow this needs to be stopped.
