If you center your eye in the scope the small amount of parallax is not going to make you miss an animal at 600 yds. You would have to take the worse possible viewing angle through the scope and even then it's not likely enough. Obviously if your shooting competition every little bit does matter but for a hunter with a 10" kill zone not so much.The problem is that while you may not see the crosshair moving around you still have the issue of not knowing your actual POA without eliminating the Parallax.
The Parallax issue is still there even when your eye is perfectly centered in the scope.