The airstrike cfg allows you to alter the frequency of air attacks per Ai skill level. To adjust the number of aircraft in each wave you must go to Dat/Land and have a look at the airbase flies. Each airbase cfg has a list of attached squadrons:
[AirGroup 1]
StartDate=19380101
EndDate=19401225
Squadron1Class=FBHurricaneMk1
Squadron1No=
2
The number in Bold is the one you want to change. In the stock game, some of these nubers are as high as 24!

. In testing for the Forthcoming Ops-Mod we found that 4, 2 or 1 give much better results. Jace's airpower mod also has reduced flight numbers. I think 2 is probably best.