Guns of War: Any ruling regarding using grapeshot/canister ammo?

I couldn't find any rule in Guns of War regarding using grapeshot/canister rounds in artillery, but maybe I missed them. Anyone have advice on how such use should be modeled? Should I just take make the artillery's AOE take effect adjacent to the piece/unit and treat it as an auto-hit?

I'm trying to model the army of a dwarven kingdom off the Hussites and their use of war wagons, firearms and artillery. I figure I'd treat the war wagons as a fortification when circled. I'm struggling how to model the troops manning the wagon line since all troop types would be intermixed. Each wagon might have 5 crossbowmen, 5 musketeers, 5 pikemen and 5 swordsmen. It wouldn't be a distinct unit of 120 swordsmen manning 5 wagons next to 120 musketeers manning the next 5 wagons. 

There's no rules on it written, no... Let us know what you come up with!

Treat it like a cone-shaped Dragon Breath Weapon?