More thoughts on how to make the game's victory logic correspond to the thinking of the opposing commanders:
Set up a little corner of the map at the bottom and give it a Russian garrison and supply. Make it a victory point. This is an abstraction for sending reserves from Army Group Center to the Stalingrad area. If the Germans do take this abstract victory location, the hex and its neighbors to a depth of 3, say, become frozen. (Taking the German divisions that stormed the point out of play).
The Russian player's main task, then, will be to prosecute his attack well enough that the German cannot safely dispense with 3, 4, or 6 Panzer divisions. (This would have to be fine tuned, of course.) Russian victory would result from one of two achievements: to smash Army Group Center and take Rzhev, Velikiye Luki, Belyi, Olenino, and some other points, assuming the Germans drew off enough force to capture AbstractObjective, or, if the Germans stand and fight, using all their Panzer reserves for the battle around Rzhev, to at least take something, somewhere, as a consolation prize.
In any case, forts should not go higher than 2 or 3. Nothing permanent along the lines of the forts of Leningrad or Sevastopol was constructed.
you cannot refine it