A whole lot of energy has been spent here, mostly constructively. Several have pointed out some very good points.
PaulBarnard's post to the efect of "change the shooter" is probably the best.
Next week I get new lenses in both eyes and going blind has shown me more than a few things... double entendre intended.
Carefully focusing the reticle is critical and sizing the target for the scope and power at the specific range is critical. Making a very hard black square on a very white background such that the reticle is placed against said high-contrast corner will allow the blind to see again! Just a few days ago I had to go to the local range, which I absolutely dread. Friend could not manage minute-of-moose. Simply making him use the center of his finger pad made his shooting go from ridiculous to repeatable.
Power changes should not cause a problem for accuracy, but may cause a change in hold because the increase in power shortens eye relief which forces a change in hold. Without the change, the P word...
Another variable I have seen many times involves rapidly changing weather both at ground level and at elevation. Rapidly moving clouds toss shadows and hot spots all over the place and force the eye into contortions trying to keep up.
If the op failed to see any parallax maybe he should look again...
Sizing the target to the scope is often a lot bigger issue than many realize.
