You will find many convoluted parts if you actually try and reconstruct that scenario in detail.
Its only been 'accepted' because its a mere assumption that has never been challenged by the defence.
What position is Neville shot in to accommodate the trajectories if shot in the bedroom? The shooter must have been at an elevated position. You have made 3D diagrams before with the kitchen window. Why not do one for this?
You're obviously defending all your hard work and are unable to accept criticism. You asked for comments on your theory and you have received them.
Neville could just be lower because he ducked, crouched, or crawled, your assumption that he was standing at his full height when shot is a massive stretch and constraint that you have placed on it.
I have no interest in providing misleading 3d graphics, nobody can state with absolute certainty the specifics of who was shot from where and in what position. I am satisfied that the police investigation is more correct, without being constrained by specifics, than your rigid made up on a whim scenario.
A number of issues with your theory have already been highlighted.
The only reason your scenario exists, is to try and place Neville downstairs before being shot. You are trying to make events fit your conclusion rather than forming a conclusion from events.
Your suggestion that I can't visualise something without producing 3d images is a bit silly, given my profession and my much greater familiarity of the house itself.
Sometimes you just have to stick your hands up and say, fair enough, I'm probably wrong. Like the box/file and bullet manufacturer discussions.
A pattern is forming.