If a properly fitted shotgun is supposed to shoot where you are looking and the key to hitting a target is to apply hard focus to the target, then why are we often behind every bird? Can you square this circle for me?
There are two issues at the heart of your question.
First, you may be stopping or slowing your muzzle just prior to the breakpoint. This is most commonly caused by an attempt to measure the barrel-target relationship at the end of your “stroke,” just prior to shot execution. Essentially, you are attempting to consciously measure and apply the appropriate lead, otherwise known as aiming. When you measure or consciously impose lead, you are softening your acute focus on the target in order to see “the gap” between the target and the muzzle. This softening of focus causes you to visually disconnect from the target, slow or stop your muzzle movement and results in a miss behind. The solution to this issue is good visual flow-through on the target. Watch the target break! Watch impact!
The second potential cause of consistently missing behind is “database” related. Each time you successfully break a target with your shotgun, it’s like posting a new target picture to your iCloud photo album. Over time, as you shoot and practice more, your subconscious database of sight pictures grows wider and deeper. As your database grows, the occasions in which your subconscious imposes the correct lead will increase.
Novices to mid-level shooters in particular tend to have an underdeveloped database relative to longer distance targets. There is simply no substitute for time behind the gun, practice and breaking more targets, particularly when it comes to longer distance targets. The more targets you break, the more voluminous your database becomes. If you are a sustained lead shooter having trouble with longer distance crossing targets, one technique you might want to try is pull-away. For shooters with an underdeveloped database who tend to measure, pull-away helps the shooter resist measuring or “checking” the barrel-target relationship at the end of the stroke. As you shoot more targets and apply good visual follow-through, your challenges with missing behind will fade.