Whaaaaaaat? The A has two extra mounts?!?! Fuck me...
That's devastating.
@Beerjerker is correct. With the ball and canard turret, you end up 2 x s1 on the canard, 2 x s2 on the ball, and 2 x s3 on the wings.
Put the flashfire on and you can mount a single s4 to the ball turret.