You can also use BOIDS behaviour and use that to "flock" your entities. They will perhaps overlap, but quickly adjust themselves to be more in a "loose group" depending on the settings you put into the behaviour.
You can get the original BOIDS behaviour HERE
You can get Rex Rainbow's version of BOIDS behaviour HERE
Each behaviour listed above works slightly differently. Rex has a bit more control but I find slightly harder to use (which usually comes with having more control).