Well, now you do see the answer of the good old question what would have happened if the allies aided Poland right from the beginning (or became active much earlier to contain german agression...) - a really great implementation of the what-if 
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Historically, when Germany fought Poland, they had almost no forces along the border to France. They just bet everything on the fact that France wouldn't invade. They were mostly right. So it isn't that strange to me that the game reproduces this aggressive force deployment, if in fact it is intentional.