Although I can't cite the source as I long ago lost it, it was pointed out that civil war losses were caused 95% by fire arms (rifles, Muskets and pistols), 4 to 5% by artillery (not the 2 to 3% mentioned earlier), and less than 1% by edged weapons (knives, swords and bayonets).
I never heard of attacking troops laying down to avoid artillery fire but I guess it happened as pointed out in posts above. But, since civil war artillery were of greater range than those in the Mexican War, it would have been harder for the infantrymen to observe the gunners movements especially when you consider the battlefield confusion, smoke and terrain factors.
Although cannister fire had a spread effect both horizotal and vertical, this created gaps which reduced its deadly effect. This spread would also put in danger any soldier who was laying down.
You may argue this but double and triple cannister was very much the exception and not general used.
Smaller field guns were less effective using cannister because they had fewer number of balls in the cannister projectile. Guns such as the 3" rifle or smaller were in this category. The larger guns were more effective, guns like the 12 pounder.
For your information, based my research of civil war firing missions, the most used range was 500 to 600 yards which was 14% of all firing ranges used. The second most used range was 400 to 500 yards which was used 11.7% of the time. Please note that these ranges were just outside of the effective range of the rifles and muskets of the civil war infantry which, I believe to have been no accident. All firing missions at ranges of below 400 yards was 42% of the total missions. This is where the fighting at close range was.
Ron
een my learning experic