Thats what happens when you have a land front, it was the same in the West after D Day, neither the Typhoon or Tempest were optimised for high altitude.The Russians somehow managed to get the Germans to fight at low to modest altitudes, where the P-39 wasn't disadvantaged. And the Russians used the advantages of the P-39, such as up close and personal with that 37mm cannon, decent low altitude speed and a decent turn radius. I'm sure some Germans knew to stay away from their opponents strengths, but maybe an overly enthusiastic command structure ordered their pilots to in affect throw away their planes' advantages.