I have noticed that ships under the formation order tend to lag behind the formation leader. I am guessing that the current algorithm dictates that ships under the formation command want to move to the location relative to the formation leader with a certain fudge factor. I can guess that without the fudge factor ships would overshoot their formation station and loop around thus falling further behind the leader.
Instead of setting the destination location for a ship relative to the formation leader’s current position, how about you set it relative to the formation leader’s future position as calculated by the current position + speed vector * arbitrary length of time. This solution works for Boids (red3d.com/cwr/boids/) and I hope it will work here.