Gotta' admit I didn't understood that.
But I guess there's even more problem. Basicly, the US lacks about 800-1000 MP in order to create a historical military organisation and it must be portioned out, so you can't have it from the start, 'cus then you'll have to many divisions, to fast and you must configure the AI, cus even if they don't invade mainland Europe (don't know what triggers it, maybe own army numbers - aixs army numbers = invade), but also the pacific, with the result of AI being a cakewalk.
If you instead decide to raise MP by adding manpower to provinces, you must calculate the daily increase and you will be able to have a way to large army, way to early. Unfortuantley, there ain't no event command that raises MP in a province when times goes by, only a one time offer (ex. add 200 MP to pool) or a percentage of current MP-pool.
So, if we want a historical game, which is one of the mods aim, one have to give US MP through events spread out over the time. But when and by how much? That needs testing.