Nightforce nx8 2.5-20x

[Achapa87]

I acquired a 2.5-20x nx8 and I really like it. Glass is pretty good and the turret is great. Although the glass is great, on higher mag it tunnels out and gets blurry on the edges. Is this common on this model or do I need to play with the rear objective. Only really trying to hear from people who actually have this model not the 4-32 as I've heard this one has a slight edge.