[Varyon]

Assuming the same type of propulsion system (personally, I'm inclined to give "fighters" drives with high acceleration and low delta-v, while "capital ships" have low acceleration and high delta-v - replace delta-v with endurance for reactionless drives), I could see a paradigm where smaller ships are narrow and long while larger ones are wide and short; the smaller ones only have a few nozzles on the back, while the larger ones are absolutely covered in them. That's at the extremes - in general, the larger you get, the shorter and wider ships are, while the smaller you get, the longer and thinner ships are.