Something funny going on in the campaign?
 

I'm not sure if it's just me, but it seems that from the second Stalingrad mission onward, the bandits are cheating. They seem to not only come after me exclusively, but also fire from further away and more accurately than they should be able to. I know I can't hit an enemy in a turn or even straight and level from over a kilometre away. Sometimes I swear I can see the bullets zipping past me but recording as hits anyway. Whenever I set myself up against similar numbers on veteran AI in training, they're much less formidable.

I can understand if this was done so arcade players could have a difficulty curve, but I only play realistic and sim, and it sucks the fun out of it. What kind of tactics should I use for the later missions if I don't want to get shot down?

If you have the chance to command your wingmen to engage the enemy, your allmost home free. Not sure if that is possible in the mission you refer to, but do it when possible.