@jim010 Seems to me it might just be a case of needing to try messing around with the German strategy, but again without a full game report I can’t really give super concrete advice.
One other thing you mentioned was that you’re not using air units in the city for fear of having them get shot down. That may be part of your issue as, in my opinion, Germany needs to be comfortable with the idea of gambling their air units to make decisive attacks against Soviet positions in the city during the initial attempt to break in, even if the air units get lost in the process. This is because:
A: you get more air units with winter storm later.
B: The “bad weather” mechanic in the later rounds of the game will eventually make your air units effectively worthless anyway.
So it’s a “use it before you lose it” kind of situation. In certain situations, the air units can be used to soak hits for tanks, as strange as that sounds.