Hi,
The eye relief problem is rather simpel. You just need to adjust the scope so you get a perfect round image through the scope then you mount your gun at your shoulder.
The best fit is then you mount your gun at shoulder with your eyes closed and then you open your eyes again you will have a perfect round image through the scope with no parallax error. Everything should feels perfect without any form for adjustment of your cheeck on the rest.
Rgds,
Thunderbolt A-10