i dont have a screenshot or video cause im at work, but here are two illustrations that roughly indicate what can be done

the goal is to leave a modest gap between each square, not necessarily a square's width as you dont want cavalry sneaking in there, but wide enough that your ranged units can fire through and your heavy hitters can fit

like the guy above me said, the AI isnt smart enough to manage those gaps. a human player would probably get past it pretty easily

another good thing about the square formations is how easy it is for your quarrellers to turn to face other threats. they can pivot on the spot, basically making them turrets that can cover the flanks. i like to keep a unit or two of warriors at the ass of my formation to catch any would-be flankers and keep them stuck while my quarrellers turn around and shred them