I realize open sights are totally different, but here is my two cents worth. In Police Academy, they taught us to focus on the target and just let the pistol sights be in the foreground and appear slightly blurry. You use shooting form to insure everything in lined up. With that being said, I have always used the rear focus on a scope to focus the crosshairs to my eye. I then use parallax to to focus the target and remove crosshairs movement. I then let my eye focus on the target without directly looking at the crosshairs. They are there and in focus, but I am looking at the target and to be honest, never really think about them being in the same focal plane. That’s just how I shoot and the only thing that appears to make might sight picture unclear, is the mirage, which is enhanced by higher scope magnification. To me, even the slightest mirage effects clarity. Our hunting scopes that go to 9 or 10 power don’t have the same effect. They appear clearer simply due to lower magnification. Like I said, my two cents worth.