Yes, but that tactic works only if you know you're going to be under attack. If the shadows were to materialize in the midst of the refugee ships, they'd just scatter in every direction. The purpose is to wipe out all those ships quickly and efficiently...so you start at the outer fringe, drive everyone inward, and then wipe them all out. To jump into the middle of them makes it very hard to do this...it's like herding kittens.
