Of course there are a lot of "mights". Your idea that Nevill was asleep in bed is also a "might", it's just that you present it differently.
The drama isn't evidence Adam, and there wasn't time to go into all that.
If you're not going to accept anyone else's point of view and their "mights", I'm wasting my time talking to you.
I don't know if the court scenes went by trial transcripts. Apart from 'that is what you have to establish'.
Obviously Nevill was in bed asleep when Bamber entered the bedroom.
The only suggestions of what Nevill was doing when Sheila got the rifle ready is sleeping, showering & watching the TV test card.
A lot of 'mights' would have to happen for Nevill to make a call while fully fit, then end up getting 4 shots upstairs, two from inches away. Too many for even Bamber to ever suggest.