Re: IOR and parallax
parallax adjustment is not a killer for shooting, it just requires you to set up the comb of the rifle correctly. By always having perfect cheek to stock weld, a fixed parallax riflescope shoots just as well as a adjustable one does.
The main issue is when you get out of prone and start to go in to sitting, kneeling.
You might would want to dial back the mag so the eye relief opens up some and lessons the parallax affect
John