I agree with what you are trying to convey. Currently there is a round shot, a shell, and a canister. I feel that each of these should have a different effect. Some effects could be decreased speed, charge prevention, reduced reload speed of targeted unit, loss of moral, decrease of condition, and a quantity of casualties.
American Civil War artillery came in 2 main flavors Guns and howitzers
Gun Cannons Need to be deployed so that they are not directly firing into units; Gun Cannon should be placed in the front of or on the flank of the front lines They should be more accurate but have less range with greater reload speed and quicker aiming, Gun cannon should also be able to use the grapeshot which prevents or hampers charge attempts.
and Howitzer Cannons made to shoot at a angled trajectory; Howitzers should have increased range and decreased accuracy able to shoot over troops and tall obstructions but require time to aim.
Howitzers should also be able to use explosive canister shot where the shrapnel is in the ball and explodes over the target
Gun Howitzers should be mainly for the Union as this would reflect there artillery and technology advantage; Gun Howitzers have the properties of Gun cannon and Howitzers.
These are some gameplay ideas that with tweaks will add content and another strategy element to the game.
http://en.wikipedia.org/wiki/Field_artillery_in_the_American_Civil_War#Smoothbores