You are correct. Most big game scopes are designed parallax free at 100 or 150 yards. With your scope being non-AO, the situation I described above certainly can't be the problem.
I'm not aware of any method to change parallax adjustments on a non-AO scope.
Before you give up on the scope, pay particular attention to how you set up your shot when changing power. I know on my VXII, the difference in how I have to position my head on the stock is dramatic when I change from 4X to 12X. This may be part of your problem.
Mike
