Jon's math is for a 90 degree crosser, I think, and any lesser angle all the way back to straightaway makes the time of flight for the string to pass the bird even more meaningless.
I've had Bill McGuire tell me to "Miss in front, if you miss. Use that shotstring." But, like Jon, I did the math many years ago and realized the same thing. It's all a matter of mere inches. The mantra to "miss in front" is really to help a shooter learn to see what extreme amounts of forward allowance look like. I find that when new sporting clays shooters miss a fast crosser (assuming they're on line with the target)they miss behind, almost always. As some shooters learn to kill fast, long crossers they reach a point to where they miss in front much more often than behind. Several of my shooting buddies have noticed this, too.
It also happens in the field. We start the hunting season on doves. Doves can easily fly over 60 mph if there's a wind. Shoot doves a few times, then go on a crow shoot and we'll be missing in front until we remind ourselves how much slower they are flying.
SRH
