In one of Stan's videos he goes over how much averting your eyes to the edge of the cue ball changes things. You may have seen it. He lines up the cb to a diamond on the long rail and shows how changing your eye focus from the center of the ball to the edge of the ball moves the perceived aim line from the center of the diamond on the rail to the edge of the diamond, or about a quarter inch. I did the math awhile back and if I recall correctly it amounted to about a 5.5 degree change. Assuming a consistent distance from the eyes to the cue ball, averting the vision from the center to the edge will ALWAYS result in a 5.5 degree change in the perceived line through the center of the cue ball. Now, this was a demonstration of what averting the eyes only would do. There was no poking or moving the head in this example. What any of this has to do with the shot line is still a mystery.