I believe that it is false to believe FS2 fighter squadrons consist only of 12 fighters. In two missions we are shown that squadrons are in fact more in the range of 5-7 wings (20-28 fighters). In the first nebula mission (the name escapes me), Lieutenant Samsa states that each squadron is sending out five wings of fighters to scout the nebula. During the mission, the Ravens indeed do have 5 wings deployed throughout the nebula.
Also, in "Love the Treason...", LT. CMD Snipes states that the entire NTF squadron you're in is being deployed to escort the Sunder, and in that mission we clearly see 7 wings of fighters at the beginning.
Also note that the GTD Aquitiane only has six fighter squadrons (Hammerheads, Ravens, Suicide Kings, Barracudas, Raptors, and Blue Lions), which when 156 fighters are divided among them, gives you 26 fighters per squadron, equalling 6.5 wings per squad (some squads may be larger than others).