Yeah, I didn't notice that it was the circle effect that was making it difficult, but that makes sense. The hell hounds' away movement seemed a bit better in that regard; though they go all the way to the other side of the screen, which the souls should obviously not do.
But maybe a movement for a little bit in a straight line away from the unit, rather than just directly as the unit moves, pixel by pixel? That would allow the player to circle around them and push them all towards the same point maybe? I think you'd have to test out some different methods to see.
Another possibility could be to have a box collider that rotates with the unit's movement direction so that the flat edge is always facing the direction they're moving, and then using that as the thing that makes the souls move, so you have a larger area of effect for pushing?