Atticus's best cover is, in fact, the natural angle of the hill from where he is, the flatness at the top of the hill cutting off half a body's worth of height for a shot. He ducks low, and Madcap can follow. A thwap can be heard from afar, and dust and rock flew from behind them as the shot missed.
They were out of line of sight down here, but on foot, it was a dangerous fifty yard run up the driveway to the house proper -- and in those yards, they'd be wide open for fire. What creativity would the Axe aspirants come up with?