Just a little info im not sure if it helps.
On Sep 13 daybreak was 5:25am and sunrise was recorded as 6:54am.
The morning after MH went missing daybreak was 5:56am and sunrise at 7:26am.
MH was last seen approx 9:30 am the night before. That is alot of time before the cover of night is over and yet she was still found so close.
If HG was last seen at Temp approx 1:45am, that doesnt leave alot of time before light to kidnap, rape, murder and dispose of a body.
IMO he wouldnt have wanted to be seen in the daylight hours travelling. Just on that alone leaves onlt a few short hours to commit the crimes. If he is responsible for MHs kidnap and murder also then history would suggest that given even a large amount of time he prefers to not spend alot of it travelling long distances to dispose of a victim. Short and quick, in and out undetected.
I do think the 8 mi radius was a good start, i think she could be furher out than that. But i dont think by far just based on the limited hours.left in the day.
All JMO