Police placed the rifle on the body in different positions, and then removed the rifle so that it was not resting on the body for any great length of time, or period, hence why there are no visible corresponding marks upon her legs, thighs or any other part of her body. The weight of the rifle on the body would have exerted sufficient pressure to create marks which fall into the HYPOSTASIS category..
Lets say that but for the police being responsible for moving the guns barrel so that it was / is resting directly against Sheila's neck / throat (in the following image taken by PC Bird during the stage managing process) the pressure of the guns barrel against or upon Sheila's neck, would leave a distinctive mark there, where none exists because police rested the guns barrel there against the left side of the neck on a temporary basis whilst taking photographs for the investigation...
Well...
the weight of the rifle resting anywhere on the body for any lengthy of time, say for between 4 to 7 hours, without being disturbed would almost certainly have left such marks on the relevant parts of the body, and the point I am making is that no such marks exist or are visible on those areas of the body, because police stage managed Sheila's body, it was not stage managed by Jeremy or any other as yet unidentified killer, and the rifle did not fall into that position upon the body if Sheila took her own life. What we are dealing with here, is wholesale stage managing of a body at the crime scene, where the police put the rifle on the victims body and then took a series of crime scene photographs which were later shown to members of the raid team at a de-brief held at Witham police station that same night, and members of the raid team were told to write up their reports as though they found the body in the position shown in PC Bird's stage managed pictures...
Now, the matter does not end there, because it was these very same stage managed photographs which were taken by PC Bird, which were used during the trial as part of the prosecutions case, to persuade the jury that Jeremy had stage managed Sheila's body on the bedroom floor after he killed her and the others, with a view to fooling the police into thinking that Sheila had taken her on life, when all along the photographs actually depict what the police had been responsible for doing (stage managing the scene to make it look like she had shot herself twice with use of a semi-automatic rifle)?