You can prevent the Allies from strongly reinforcing Russia with fighters by threatening Vyborg and Leningrad early. The only efficient way for the Allies to get fighters to Russia is through Leningrad, a distance of 4 from UK. Fighters built in the US on turn 1 land in UK on turn 2 and Leningrad in turn 3. They then join the Russian stack in Belorussia on turn 4. You have until then to make sure you have enough forces forward to ensure that the Russians can’t stand in Belorussia even with all the extra fighters. Further, funnelling fighters through Leningrad means the Allies have to divert ground units from Belorussia to prevent everything from being lost. If so, the German player gets to choose which battle to fight, Leningrad or Belorussia.
The other thing you can do is try to get the Allied player to divert fighters to the Battle of the Atlantic by using you subs in sea zones where it disrupts the flow of fighters to Leningrad.
If the Allied player has been able to get 7 or 8 extra fighters to Russia by turn 3 or 4, Germany is probably doomed, so a combination of pressure and diversion usually prevents the fighter build up.
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