We're you using scope covers on your mk5? I have a mk5 5-25 and had factory lens caps installed and just replaced them with the Tenibrex covers and now I have a very large black ring around my objective as you are describing. Going back to the factory included caps.
I have had very good results with them out of a 6.5 CM factory loads @ 2695 fps. Nothing has went more then 10 yds before dropping. Ranges 150 to 356 on deer and speed goats. Pics below of a whitetail at 150yds, massive blood trail went 10 yds and done.