That is what I mean when I say a typicall KGF-all out against Germany just won t work most of the times.
With japanese air in Europe, UK-US will end up creating one loaded AC (UK AC and 2 US ftr combined IPC 34) for every 3 japanese airplanes in Europe (IPC 30-32). At the same time, the Allies must stop Germany in Europe (by offloading 4 UK inf and 6 US inf=combined IPC 30), something that is doable untill Africa falls to Japan.
This consumes all UK-US income in order to stop Germany in Europe and match the japanese air reinforcements. SO, we have Russia and the remaining Japanese forces. Russia alone cannot kill (a reinforced by japanese air) Germany. But it can make sure to hold Ukraine and garisson Novosibirsk, keeping the Japanese at bay.
The obvious move for Japan is to go after Africa. Russia cannot reach the japanese forces landing straight in AngloEgypt Sudan. And with one blow it cripples the allies’ ability to both stop Germany and to match the japanese airforce in Europe.
The thing is imho that while everyone else is totally reactive (Germany is all out stacking ground defences, UK and US are all out stacking gound and sea defences, Russia is all out to hold Ukraine and novosibirsk) in Fortress Europe Japan has the chance to be partially proactive. After sending the air reinforcements in Europe, the remaining IPCs can be used in a way that the Allies have nothing to respond.
That is why most Fortress Europe games end up with Japan taking Moscow after having raided Africa, while the Allies are stuck way outside Berlin. In some cases, Moscow is traded with Berlin, meaning they both fall in the same round. In fewer cases, Berlin falls just in time before Japan takes Moscow. But there is almost never a clear Allied victory with Fortress Europe.