There is variability in every group that you shoot. The smaller the group shot count (3, 5, 10, etc.) the more variability there will be. If you're shooting 3's or 5's you can have tons of variation. One group can be 0.9 MOA and the next can be 0.3 MOA.
Your 2 MOA group at 200yd is NOT the same as your 1/2 MOA group at 800yd. Different conditions, different random distribution of shots, different parallax error, etc.
If you want to put it to the test, put paper up at 100yd such that the paper hangs just above your line of sight of a 500-600yd target. This will allow you to shoot a group at 500-600yd then see the SAME group at 100yd. If you EVER in your life get a smaller (in MOA/Mils) group at the further distance, please let the world know.
Once a bullet is on its vector, it will not change unless acted upon by an external force. That vector is random (dispersion) and is set as the bullet leaves the muzzle.
To consistently produce 1/2 MOA groups at 800yd and 2 MOA groups at 200yd requires extraordinary circumstances that are most likely related to shooter skill, optics, etc... Not the accuracy potential of the ammunition and rifle.