You forget how long the rifle was, even longer if you believe a moderator was fitted. And if most of it was held over the bed, even more likely that the ejected shells would land on the carpet between right bedside and wall cupboard.
Nevill couldn't have been shot in the face while on the stairs or lower landing by Sheila (or Jeremy) standing on the upper landing. The casings would have finished up on the steps of the main stretch of the Hall stairs, and not where the two found are shown on plan.
I've never known the length of the rifle with or without silencer. I did attempt to find out online and looked at the parts diagram you posted but to no avail.
If NB was lying prone with JB at foot of bed wielding the rifle over the bed so that the end of barrel/silencer was within a few inches of his skin, I fail to see how NB left the bed let alone the bedroom. Especially given the rifle was a semi-auto.
You've just reminded me how long the rifle is with or without the silencer. If SC was stood just inside the entrance with the ejection port also inside the bedroom and the barrel extending out onto the landing, angled at 20 degrees below the horizontal and pointing at NB's face whilst he was stood on the stairs immediately preceding the entrance, I think it's entirely feasible he sustained the lip and jaw shots in that location. The casings, as we know thanks to your vid, eject forward and to the right so this could account for DRH/3 and DRH/4.
I can picture in my mind's eye this scenario best by looking at the following photo.
As far as I can see it's the only scenario that fits with:
- Trajectories - 20 degrees below the horizontal as per Dr Vanezis' autopsy
- Wound tracts - lip and jaw face on as per Dr Vanezis' autopsy
- Blood staining on carpet - as per DC Hammersley - SoC officer
- Casings - as per diagram
- Distance of shots - a few inches from skin as estimated by Malcolm Fletcher/scientific officer for ballistics