Hi Sid, my information is that the post-war zones of Allied occupation were worked out in November, 1944, by the European Advisory Commission consisting of American, British and Soviet diplomats.
Apparently, the German High Command learned of the occupation plan from a captured copy in January 1945. Captured with it was a letter that spoke of unconditional surrender and the dismemberment of Germany.
Remember that it wasn't until Jauary 20th that Soviet forces actually set foot on German territory. The question of Poland's borders is a complicated one and I'll post later on that.
Best Regards, David
Death is lighter than a Feather, Duty is heavier than a Mountain....