I do know why the units do this. It rests in the method used to program group movement.
Think of each man in a unit as the X of a bullseye, with 2 rings around it. The outer ring is a Zone of Attraction. He is attracted to all the other men in his unit. (don't ask don't tell!!) So he will merrily skip and run to the other burly hairy man under the same mon banner.
But wait! Suddenly he's so close to the other samurai that the other man is within the inner ring: the Zone of Repulsion. (Probably because he's now so close that he can tell the other man hasn't bathed in a few weeks.) The Zone of Repulsion works on everything, not just his fellow mon-mates like the Zone of Attraction. The Zone of Repulsion is also stronger than the Zone of Attraction.
So that's how they end up all nicely spaced-out within the ranks. There's a balance between the Zone of Repulsion and Zone of Attraction. When something else gets in the way--a tree, a cliff, or another man from a different unit--they are repelled. There is probably an additional Zone of Repulsion for friendly units in STW and some code to handle "mass repulsion"--if enough men in each unit are having to shift around enough, then just move the whole damn unit.
I have seen, though, units which weren't mingled, moving around on their own. So apparently the Unit Zone of Repulsion extends beyond its own ranks a bit for some Liebensraum.
Bookmarks