I strongly believe that where Karen was found was where she was initially dumped.
No one under such scrutiny would be brazen enough to return and move the body and give themselves up... Especially given the media coverage and exposure this case has had.
Here's my 2c - let's assume she was moved to her final resting place from the family home (the last place she was known to have been). This would have meant she was murdered somewhere else in the house. I'm sure police would have searched for blood - nothing. No skull/bone fractures (rules out the "falling down the stairs" theory for me). I'm thinking poison or suffocation with something like a pillow. But with strangulation or similar, you would expect some form of wounds/scratches to BR -- but he doesn't have any. This points once again in the direction of Karen being poisoned, unsuspectingly (duh!). Not a scrap of evidence anywhere in the home (that we know about, aside from the shovel).
She's then moved into the garage and into the boot of her car, with her hand bang and phone to make things look less suspicious (she went for a walk to clear her head - remember? She would have taken these things, as most of us would). Her car is chosen to move the body because it's more likely that her DNA is found in the car she drives daily, as opposed to BR's vehicle. Most people would seek to distance themselves as far as possible in the shortest amount of time to avoid detection; hence, BR takes a drive up the Calder Freeway. He drives off the beaten track to somewhere quieter -- Karen's final resting place. The phone pings support this.
He tries digging a hole to conceal the body, but deep holes are hard to dig -- especially in the black of night. So he does the next best thing that any logical person would do - he conceals it in the immediate environment as best he can; between two fallen trees. He covers her, as most killers do when they know the victim, to both conceal the body and to comfort himself by not having to continue to look at the body.
What happens next is a mystery to me - where is KR's phone and hand bag? If these items are found with the body, this lends credence to the
possibility that she went to this place herself and commits suicide. If the bag and phone are not there, then it's obvious that the body, phone and hand bang have been disposed of in different areas.
Another mystery here is motive - financial, secret lover, complete accident?
But what do I know?.. I'm just an arm chair detective