Firing downward does make a difference. When a moron built a fancy house on a hilltop that could be seen over the top of our berm on a clear winter day, the club not only increased the size of the 200-yard berm, but also built a ridge at the firing line. Shooters on the 200-yard line are about 15 feet higher than those on the pistol range, firing down at the base of a very tall berm.
It didn't stop him from claiming that he found bullets in his exterior walls, but since he showed the sheriff's deputies loaded cartridges, they were skeptical.