From what I understand, the issue is availability. A normal squadron needs 21 jets, and I believe MKI was designed for 20 per squadron. But due to availability being what it is, more jets are needed to ensure a squadron has enough operational jets at any time. Which is at least 12. 22 jets will give us 12 at 55%. If we raise availability to 65%, then we get 13 jets out of 20, which would free up an entire squadron worth of jets. At 70%, a squadron can have just 18 jets, with 2 reserve. So the total operational fleet size can be 260, with the remaining meant for other use.