Rick,
normally the officer on the gun line would be a section officer, overseeing 3 guns. So 2 officer per battery, on the gun line.
The guns are in command of a Sergeant, and NOT an officer. Officers are usually in the command post or forward observers calling in fire missions or commanding the whole battery and regiment.
I really don't like it when makers have an officer with each gun. The officer should be a separate figure and so you could then have a realsitic setup of figures.
John