The layout diagram of WHF shows two oblong shapes preceding the entrance to the main bedroom indicative of two stairs:
http://miscarriageofjustice.co/index.php?topic=633.msg25947#msg25947
AE's WS refers to reaching the landing and going up a few steps and turning right into the main bedroom:
http://miscarriageofjustice.co/index.php?action=dlattach;topic=1053.0;attach=3100;image
There's also a photo showing a sloping handrail leading up to the main bedroom:
http://miscarriageofjustice.co/index.php?action=dlattach;topic=6697.0;attach=5920
I believe NB was stood in the area where the handrail turns or maybe on the first step and this is where he sustained the facial shots with the perp firing from inside the main bedroom.
If he was standing where the handrail turns then he would be the same floor level as the shooter and the downward trajectory can't be achieved. If he was standing on the stairs then his right side would be facing the bedroom doorway. He was shot from the left not the right. The legends I provided detail where the shooter would be in relation to Nevill. The first one was with the shooter to Nevill's front left which is with respect to the face shots and the other is with the shooter to his left rear which is how the other two shots were delivered.
If you use such you would see that someone walking up the stairs could only target his face if standing by sheila's door. Pretend the dot in the middle is Nevill. He is on the stairs. The blue field is where the shooter would have to be in the hallway.

You can rotate the image depending upon where you want to stick Nevill. If Nevill were facing the master bedroom door the killer would have to be inside the room somewhere near the chair:

The blue field shows where the killer had to be when firing at his face and the red field shows where the killer was to fire the arm shots.
The ejection port is within the bedroom with the casings ejected slightly upwards and to the right hence DRH/3 and DRH/4 are located just inside the main bedroom. The following photo shows this is a distinct possibility:
http://miscarriageofjustice.co/index.php?action=dlattach;topic=6697.0;attach=5920
They eject at between 1 and 2 o'clock. The eject hard they don't just travel a little. They would not land where you claim and more importantly the right side would be targeted if someone were on the stairs and if walking in the room then the killer would have to be where I showed.
This is the most plausible explanation for the trajectory of the facial shots ie 20 degrees below the horizontal.
No your theory fails to account for the downward angle to a shot suffered while on the landing. Only oon the steps could the angle be achieved but on the steps the left side would not be targeted.
The most plausible explanation for the trajectory is Nevill was seated on the bed or in the process of getting up when he was shot in the face. The cases were found where they would be expected to be if this is what happened.
I believe the shots to NB's shoulder and elbow were sustained whilst NB had turned and was facing down the main staircase with the perp behind him. The pathologist's report states:
Entry wound measuring 3/16" situated 1 1/4" below the point of the left shoulder on its outer aspect. The track of this wound was downwards causing a comminuted fracture of the upper third of the humerus with considerable overlapping of the fractured from soft tissue near the fracture site.
Oblique grazing wound measuring 1/2" situated 4" above the left elbow and associated with surrounding bruising. The track of this wound was from the left arm and against the left side of the lower chest causing a 1 1/2" graze with a curved edge which was 3/16" in width. The radiograph showed fragments of a bullet in the left lower chest although these could not be located within the body cavity.
The above relates to wounds 7 and 8.
http://miscarriageofjustice.co/index.php?action=dlattach;topic=199.0;attach=676
Image of humerus below.
It seems to me NB sustained the grazing wound when the perp was behind him since it bruised his left elbow and bullet fragments were found in his chest cavity. I can't see how these injuries occurred from any other direction?
I showed you where the killer had to be in order to fire the shoulder wound and graze wound. The killer had to be in the red field.

No the outer aspect is the side of the shoulder. You can't hit the side of the shoulder if you are directly behind someone you must be to the side.
The graze wound went left to right into his side, that can only be achieved with the killer at nearly a perfect 9 O'clock position. My clocks above are is a little flawed only with respect to the fact that the trajectory of the graze would could be 9 or a little more than 9. The red is really the trajectory of the shoulder wound. The shoulder wound was more to the back than the graze wound was. The green is the area where the killer was to fire the graze wound:

It should be obvious to you that when Nevill is walking down the stairs the wall is blocking the killer from being able to target his left side. Thus the wall prevents the necessary angles from being achieved. You have not taken into account the location of the bullet that grazed Nevill. If he had been grazed while oon the stairs it would have been on the stairs not in the bedroom. But again the only way to graze him while he is on the stairs is to shoot through the wall.
The location of the casings and bullet and downward trajectories all support Nevill sitting in bed or in the process of getting out of bed when shot.
Again with the casings ejected slightly upwards and to the right I believe casings DRH/13 and DRH/14 landed on the transition strip to the main bedroom and the landing.
That doesn't make any sense. Moreover, DRH/14 clearly was from the kitchen which was missing a casing.
Scipio as far as I can recall I've only ever stated no evidence exits of NB's blood in the bedroom? The two blood stains on the landing carpet DRH/47 and DRH/49 were inconclusive. The lab required two positives to confirm a conclusive result. They were only able to get an 'A' and 'O' grouping result on the carpet samples from the landing. NB's grouping was 'O' and June's 'A'.
On blue there was a post confirming DRH/49 was Nevill's blood. that in turn was used to support allegations that Nevill came out of Sheila's room. I didn't save the docs because it is inconsequential. The hallway is not big it doesn't take much to reach the location where it was found from the bedroom. Nevill could easily have ran towards Sheila's door before going down the stairs and also the killer could have had a drop of his blood which dropped off. Whichever is the case makes no material difference.
They didn't test all the blood on the bedding and carpet in the bedroom so there is no way to know if Nevill's blood was there or not. Being shot there would not necessarily result in his dripping any blood in there. When you bleed from the mouth it moreso gets on you.
The only reliable evidence of where he was shot are the casings, bullet that grazed him, trajectories of he wounds not just the casings and the entire circumstances. June would not be sleeping in bed while Sheila was running around with a rifle. If he got up to go check on things then he would have been shot elsewhere before June was ever shot.
How could a bullet graze Nevill while he is on the stairs then do a u turn back up the stairs and another u turn into the bedroom? How could a bullet scrape the back of the arm and then hit the side unless it were fired from the 9 o'clock position? How could someone walking down the stairs be shot from the 9 o clock position other than through the wall? The clocks I provided show the location of the shooter vis a vis Nevill for all 4 shots. The angles are not possible with Nevill on the stairs unless the killer was near Sheila's door but the casing location don't support such either.
You asked why the defense didn't challenge the assessment of him being shot in the bedroom and this explains why.