Mike, you have to be able to see the bird, unless it's a dead overhead, oncoming shot. My guess is that when your brain thinks the tip of your barrel is low, what's really happening is you're lifting your head (seeing more barrel & making it appear low) & actually shooting high. My experience has been (with birds dangling legs that have crash landed further on, or been knocked down w/ 2nd shot) is that a dangling leg doesn't necessarily mean their leg has been hit. I've cleaned lots of these birds that had absolutely nothing wrong w/ their legs. I think they just drop a leg sometimes if they've had a bb whistle through them somewhere. Also, when they're flying, the legs are tucked up & basically almost in line with vitals & stuff (as far as a shotgun is concerned). Straight-aways are just plain difficult if they're over 30-35 yards. Easy enough to hit; tough to kill. Pellets have to penetrate through a lot of crap (literally) to get to the boiler room & their heads/necks are well shielded.
Brent, I would buy what your saying about about lifting my head....thanks for the advice....Your so right about those straight-aways....I've POUNDED birds flying straight away thinking "That's a dead bird" and my dog ends up on an 80 yard retrieve.