I am struggling to understand the problem but I think it is either:
1. You are not altering the sidewheel when you put the mag up - so the image is blurred on the higher mag (as Dave suggests above) or
2. You have not mounted the scope correctly - the eye relief changes slightly as you go up the mag. If you have set the eye relief at its furthest point when on low mag then when you put the mag up your head is not in the correct position. The solution to this is to remount the scope and set the eye relief with the scope on its highest mag setting.
3. you may not have altered the eye piece to focus the ret correctly?
Or - all 3 of the above????