If you have and adjustable stock, eye relief is less critical. I usually set my scope eye piece even with or just forward of the back of the charging handle. This keeps the rifle somewhat tight (compact) with adjustment room both in and out. My neutral position is my nose about one finger width from the charging handle. If I'm shooting prone, I adjust the stock out a click or two.

With my NX8, I had the set the diopter on 6x. This was the best compromise, setting it at 8x would jack up 1x for me by causing reticle doubling. There was no perfect setting.