I only Caledonians method when defending against overwhelming odds. Usually a U-shape formation of spearmen around the gate and some archers and heavy infantry on the walls is enough to completely wipe out an enemy army with minor losses, which means less then 10% and usually even less. I never use the schiltrom formation. I prefer the U-shape formation. Any enemy that enters this formation will automatically route. I usually lose more men to while waiting two turns before the enemy attacks then during the actual battle.