The acceleration of fleet members is less of what it should be, they also seem to have an issue with keeping up with the flag ship because they slow down as soon as they reach their fleet position.
There's another issue where fleet members do 180's periodically even though they shouldn't, most likely they overshoot their target point that doesn't update in time?
I'm not sure what exactly is causing the slow acceleration but it seems to be unrelated to thrust/mass ratio at least.