AA in the game, seem to use a kind of 'barrage fire' where they just put a number of rounds into a volume of space around the aircraft. You can see from the video above, that this is the least effective flak method, and that evasive procedures by pilots do not improve chances of avoiding flak. It would be useful to be able to tie the AA battery units together (maybe with the 'set' button, and be able to select the firing methodology (3 types) from a 'director unit'.
A request for improved flak AI has been lodged at Il2BugTacker
HERE