As long as the aiming eye's kept on the optical axis of the scope, there will never be any parallax of the reticule on the target's aiming point regardless of where the objective (front) lens group's focused.
The issue is that most people are really poor at keeping their eye at the center of the optical axis of the scope.
Also, what do you consider the optical axis?
Are you talking about the external glass, or the erector?
These two are rarely aligned unless you have a scope that adjusts externally like they did 100 years ago.
When teaching new precision rifle shooters, I find that they make their greatest leaps in precision when they fully understand how to adjust their parralax to remove all parallax error.