Usually, below the troop formation.
"During the Civil War, some artillery commanders used a technique in which cannons were aimed at the ground in front of advancing enemy troops. The exploded canisters struck the ground, and balls ricocheted off the ground, expanding the target area. Union artillery effectively used this technique at the Battle of Gettysburg"
"Good results can be obtained at from 300 to 600 yards, but the maximum effect is produced at from 300 to 450 yards. When firing at very short distances over hard, dry ground, a suitable dispersion of the balls may be produced by firing very low, and allowing the balls to ricochet."
-ARTILLERIST'S MANUAL