Yes, 93mouse did over-intellectualised the business but that tutorial has some value. It touches on matters like the eye automatically centring the foresight and eye fatigue that probably troubles target shooters. I'm surprised it doesn't mention the ability of a small aperture to sharpen your picture of the bull (I'm myopic but even without my glasses I can still resolve distant objects by peering through a pin-or-nail hole).

What is not mentioned is that for fast shooting with a large aperture, you really need the rifle to fit you so well that the rear sight is almost irrelevant. Otherwise, when in a hurry you really can let off the shot without having the foresight centred. So, don't look for the blur - have it will find you.