It seems to me that it is definetely beneficial to attack from multiple angels if possible, since when your seedlings attack they will get attacked from 2 sides before they have reached the astroid and adjusted into attacking. Splitting your forces into 2 groups let one group arrive relatively unharmed.
It may also be good to attack with a small interval, sacrificing a few seedlings in order to let the enemy seedlings focus on them and letting the bigger group after them be unharmed before they touch the astroid.
Or maybe you could even time your attack in such a way that they arrive when fewest enemies are on the designated spot of arrival?
A small attack force makes the enemy seedlings cluster more, so that you can better time your attack.
Also higher speed makes them adjust quicker I think.