The shots to the lip/law were also at a downwards trajectory. Read Vanezis trial testimony. I have attached the relevant transcript in this post.
I think it's a case of making uneducated assumptions.
The bullet tracts being downwards does not necessarily relate to the trajectory of the bullet before it struck it's target, just the route it took after hitting bone.
In any event, Nevilles head would/could have been lower than the rifle whilst he was in the bedroom, the shell casings indicate that he must have been shot in the main bedroom.
I don't actually see how suggesting otherwise aids your cause.