To answer your questions, Omni, mass determines how the ship will behave when hit by high mass weapons and in collisions (a really low-mass capital ship will act retarded when it's being fired at; a high-mass fighter could ram a small capital ship out of position) but it has no bearing whatsoever on ship AI. The class ("cruiser", "corvette", "capital", "supercap") *does* affect ship AI on a rudimentary level, but things like collision avoidance and optimal facings are beyond the scope of Freespace AI. For that matter, look at fighters; they are notorious for slamming into things (including each other) for no apparent reason, and the only reason that they even look like they are intelligently attacking capships is because they follow pre-defined paths. However, you do NOT want to set a 800m+ ship as a fighter; I'm suprised the AI hasn't already rolled over and died with the Defiant model.