JDW, I agree with Chuck about seeing the barrel. If you don't see the barrel(s), end of the rib or something, there is now way for your brain to determine lead. Lead is the distance in front of the bird to something, that something being the barrel(s).
Many people confuse not LOOKING AT the barrel, which should absolutely never be done during the shot, with seeing the barrel. You just cannot establish lead, be it by sustained lead, pull away, or even spot shooting, without having the barrels in your field of vision. Even when I shoot a free bird from the hip, or when Tim Bradley, the new exhibition shooter, shoots a bird with the gun over his head, the barrel is within the field of vision and is seen, providing a reference with which to establish lead.
If you really believe you are not seeing the barrel you are probably doing a great job of focusing on the bird. That is a GOOD thing, but that focus can fool us into believing we don't even see the barrel, which we must.