It's probably not even that complex, but it has been far too long since I did geometry so you'll have to work it out yourself.
I mean you'll basically be just working out what is the green area enclosed by the blue lines (shots that will hit), minus whatever areas there are where your shot could fall short, overshooting is obviously not a problem as that'll hit the target (for ballistic weapons, anyway), compared to the green area enclosed by the black lines (total scatter area)
Circular segment with h being vertical scatter centered on the centerpoint of the enemy unit and theta being scatter angle, blue lines angle is probably fastest to just approximate, though you could of course calculate it from the simbox size of the enemy unit.
Thanks! I can easily calculate that.
My only issue now is how do I get the dimensions of the