Re: Optics question
Sounds like a difference in eye relief (i.e. distance from your eye to the first lens). Either the new scope is mounted so that it's closer to your eye when you're in shooting position, or the scope itself is capable of longer eye relief. I haven't scientifically examined this but it seems to me that some lower end scopes allow for greater eye relief.
Try getting in normal shooting position with your Nikon and, without changing your hold, slide your face forward without breaking cheek weld. If it the "window" goes away as you move closer, you may want to think setting your scope back a little closer to your eye.