I think it's just the extra field piece per battery one gets that makes it seem faster. I'm usually attacking with less men so I try to entice the enemy to come to me by attack/occupying a town/farm/industrial area especially when I only have fixed artillery. Some battle maps give you better terrain than others, and this Westphalia battleground was ideal even without the chance to construct fortifications. Nothing like high ground with a cliff on one side to place a battery with infantry in front and below out of the direct line of fire.