You're confusing resolution and virtual image size. Virtual image size of an immersive display system (video headsets) is the equivalent of the diagonal of a s

You're confusing resolution and virtual image size. Virtual image size of an immersive display system (video headsets) is the equivalent of the diagonal of a standard scren. Virtual image size is typically quantified by the Field of View (FOV), and is typically expressed as an angle your eye closes with the diagonal edges of the virtual image. Pretty much what you describe. Another way people express virtual image size is by saying e.g. "a screen with a diagonal of X cm (in) at a distance of Y m (ft)". This may seem more intuitive at first, but problem with that is you can use different combinations of X and Y to express the same virtual image size. This is why FOV is a far superior way to quantify virtual image size.