IMO the best use of organ guns, and one I've used quite often with great success, is at the front corners of a "demi-hexagon" defensive position. One thing to watch is the steepness of the slope - if it is TOO steep the OGs won't fire, as they can't target very far below horizontal. A gentle slope is better as it gives a range advantage and still will fire. They can do terrible damage and inflict those morale penalties as well. But then again I do have quite a taste for artillery in defence