Mutual attacks - where do they fight?

[Tris]

That isn't what you are suggesting.

Yes it is!

I would see this in game as the big army being unable to form into march column without little bits being hit by hit and run attacks, supply columns being hit by raiders, so the main army must spend most of its time foraging, rather than marching, and must provide patrols to guard each foraging party, or have them go missing...

The net result of which is that it is difficult to move a strategically slow army when under constant attack from reasonably large and strategically fast armies.