It'd be neat if you could merge units into combat groups (to simplify control of large battles) and split off detachments, so that 1 full strength unit could be in 2 spots if it made sense. Then looking for small groups of men, scattered could be portrayed more sensibly, and you could do something about it.

Perhaps one reason Velites are good Infantry for bagging routers, is their natural width, more chance of catching the spread individuals.

The engine is letting itself down, when you see several units, running in formation after a routing unit (also in formation), and when the units are merged into each other with both in close order, it looks even worse.