Just luck of the draw I think mark. You could hit the boiler room all day long, and some will hit the wing and bugger off 50 yards. Others will drop like stones.
The natural reaction I guess. Surprising really, as I could get shot in the chest with a 303 say, and I bet you 20 coins, I do not manage 5 yards let along 50.
As v'man says, head shots tend to drop anything on the spot.
Nice spot that though.