For some reason I was under the impression that all sizes of Gauss Cannon were allowable for fighers. I just discovered that full size (6HS) systems force a fighter component error. When looking at the tables for tech items I don't find and control flag for this, so I'm assuming that this is a hardcoded item. Mass related?
What is the breakpoint value? Could you add something to the design panel to warn if a GC design won't be allowed in a fighter?