I think Poland is an ideal location for a G1 IC:
1. It’s closer to the Eastern Front
2. It’s easily defensible (the bulk of your units will march thru there on their way to Moscow)
3. It’s not an auto target for the Allies (like France is)
4. It’s further from the established US/UK sea lanes and therefore less likely to be attacked
5. It’s “safer” from SBR, as it can only take 6 damage
6. You don’t need 16 production capacity (just buying infantry costs 48 IPCs–by that time you’ll have a SU IC)
Further, a good G1 buy would be IC (15), 4xInf (12), Arty (4). That gives you 5 units to start your push East into Poland on G2. Assuming about 45 IPCs for G2, you can then place 3xInf in Pol, and 7xInf and 3xTank in Ger. That means you have 8 ground pounders in Pol on G2 (compared to 10 for the “typical” G1 build of 9xInf, Arty), so you’ve only traded 2 units in the short term for 3 units every turn for the rest of the game.
Also, let’s compare a G2 buy with a Pol IC to one without (and assuming 45 IPCs).
G2 w/ Pol IC: 10xInf, 3xTank
13 units, 19 attack power, 29 defense power
G2 w/o Pol IC: 6xInf, 3xTank, Bmb
10 units (one can’t hold ground), 19 attack power, 21 defense power
A French IC would let you buy 15xInf, but you get 4 less attack power, and only 1 more defense power; plus you will struggle to “max” those production spots, especially once you capture a Russian IC. I’ve ruled out the Nwy IC as too far off the beaten path to be worth it for Germany, and it would be hugely detrimental if the US could capture it (which they could relatively easily.
Just my $0.02…