timelinex, I disagree with your premise in the following:
While the parallax knob is often used to 'focus' the target at different distances. That is not the actual purpose of the function, and is actually an incorrect use for it. The parallax adjustment is meant to put the optics in the same plane as the target. Which in turn makes your sight picture parallax free.
But I'll address in in a new thread titled "Parallax Knobs; A Misnomer???" so this thread won't be hijacked.