.....I've used various AO scopes on my .22s for years at ranges from 50 feet to 125 yards and have never had a target out of focus after I've adjusted the eyepiece........
Note the italics. Having to adjust the eyepiece is no different than having to adjust the yardage on the AO. Also, note step #4 form the post by fancypicker. A non-AO scope, although parallax-free at a specific distance, requires NO
focusing adjustment of any sort - if it's a quick shot hunting situation, one thing you certainly don't need is to focus the scope... regardless of whether it's the eyepiece or the yardage.
The italics were to emphasize that focus comes from the eyepiece, NOT from the objective lens. ALL scopes, regardless of AO or not, must have their eyepiece lens focused to the individual user. This needs only be done ONCE for each shooter and the eyepiece can then be left alone. I disagree with the poster who put that as step #4. It should have been step #1, and it only has to be done once. The only time I ever have to mess with my eyepiece is if I decide to switch to using the scope while wearing corrective glasses, or not.
If your eye is dead center behind the scope, there is no parallax error, no matter the range.... and, unless your eye is nearly to the edge of the exit pupil, and at long range (since the error is determined as an angular error) the error is insignificant.
You are correct on the first part, if your eye is in exactly the same place every time, you will have no parallax error. Unless your stock fits you exceptionally well, though, this is very difficult to achieve.
And I disagree that the error is insignificant. It can be quite
significant. I had yet another example of this last week. My son and I were shooting one of my rifles (a CF) with a big-game (non-AO) scope with the parallax set probably at 150 yards or so. We were shooting at 50 yards just to get it on the paper and test some ammo. The gun's stock is NOT set up for scope, and kind of leaves your head "floating" when using the scope (it's an M14 type rifle). He and I both shot nice groups, but the centers of our groups were more than two inches apart
because we had our eyes in different places when shooting (we were shooting from a bench so hold, stance, etc. were not factors). I don't call a 2" discrepancy at 50 yards (4 MOA) an "insignificant" error; do you?