>>281104625
Yes they do maintain the same focal distance and FOV that we have with normal headsets, but are able to do it with a smaller form factor. Another reason they designed it like this is that they could place the eye tracking camera right in the center, without it being visible to your eyes. That makes the eye tracking math a bit easier to do.

However it does end up being that the optical path is still not that short. It's about 3.5 cm, and current headsets are like 4-5 cm. A big part of why headsets are still so large despite the optical path actually being quite small is really just because we want eye relief and face cushioning, and the screens and optics are flat while our face isn't. The real shrinking of form factor will come when we can get waveguide-like thin layers that conform to the curvature of your face like ski goggles. 

>>281104720
Not necessarily. Remember that in the distortion map, magnification increases with angle away from the center, so what we're really seeing in current headsets is undersampling in the center and supersampling at the periphery. What they're doing, by combining 4 views of the same image but with the opposite sides cut off, is essentially supersampling the central overlap of the 4 images.