Nevill was knocked out and fell against the Aga before regaining conciousness and being shot several times and beaten before slumping on the chair/scuttle where he received the final four head shots.
The only person to see Nevill lying against the Aga was Sheila,and she is dead,that is why it has taken so long to work out what made the marks.
Clear Adam?
So he was shot 4 times and beaten in the kitchen.
He falls on a cold aga door.
He wakes up, puts his pyjama top on. Goes back downstairs and falls onto the coal scuttle without knocking it over.
Sheila is still alive and shoots him 4 more times.