Check out the formations.txt file
Only ship you have control over is the leader. The rest are placed according to the formation, with the oldest ships getting the lowest number. Since the oldest usually also is the smallest, some of the formations can suck really bad for certain fleet combos.
On the other hand, if you have the time it can be used as a feature; retrofit your old LCs with Shield Depleaters and Engine Destroyers and they can be quite effective as the front line
