So you are talking about an internal arrangement and not releasing Poland as a puppet. If that is the case, it makes a lot more sense. Russia would NEVER have given Poland up willingly, even by releasing it as a puppet. IIRC, Russia lost 40% of its population in OTL when it lost Ukraine, Poland, Belarus. However, I do not know how much of that population lived where and much of that land, minus a large chunk of Poland, was latter retaken by the Soviets. However, I would assume a sizeable amount of that lost population lived in Poland. The only way I could see Russia even considering releasing a puppet Poland would be if threatened with a massive Polish revolt.