My knowledge is middling at best.
One thing I should mention is that my approach to the Soviets, in 41 at least, is that your units are hot garbage. 100 CPP, 95%+ TOE Infantry Divisions under a good leader are barely passable on the offensive. Additionally, your AFVs are your only real blunting tool against German Panzers.
Thus, my approach the the Soviet defence is that I'm not maximizing damage done, I'm aiming to maximize movement points spent. Ultimately the ideal situation is you bog down the Germans long enough for mud, and then reach a critical mass of troops that denies them a good 42 season - which they absolutely need or they'll lose.
Let's take the south, for example. Besides the occasional rough and light forest hex, it's practically all just rivers and flat terrain. Ideal, for the Axis player. But rivers are extremely potent tools defensively. No matter what unit is defending a river, it forces the same amount of MP to attack it. Although I advocate abandoning the south, this game I'm choosing to defend it - so these rivers are the only tool available for me to hurt axis movement. Careful positioning will be required to maximize the MP spent pushing units aside.