User blog comment:Homuhomu123/Trigger Rates & Effectiveness of Anti-Air Cut-In (AACI)/@comment-101.184.172.178-20150829065126/@comment-80.41.138.210-20150829163805

3 accoroding to jp wiki, which means you're better off using API 5 or API 8 if you have a HAFD.

http://wikiwiki.jp/kancolle/?%B9%D2%B6%F5%C0%EF#antiairfire