Dunno about that.
My Corvettes have got ventral gimballed MCs and they seem to track & fire almost all the way up to the top of my screen.
As a rule, I try to keep my MC's on-target properly, just to avoid getting lazy for when I'm using fixed MCs, so it always surprises me just how much of an arc-of-fire the ventral hardpoint has.
If you stuck a beam laser in there, targeted a nav-buoy (cos they don't get upset when you shoot at them, and they don't move) and used the camera-suite to get an extrenal view of the laser firing, I'd bet it'd be clipping though the nose of the ship, as is the case with the FdL.
If I was the OP, the first thing I'd do would be to stick a beam laser in that slot and verify whether or not it's actually firing.