I wonder whether the 'pile of leaves' comment actually came from Police or whether it's been exaggerated or misreported in some way.
Like you say, the crime scene tent, is in an open grassy area and there's not many fallen leaves this time of year unless the alleged went into the tree area and gathered up half decomposed fallen leaves from last year. That would take some time though, like you say.
I wonder whether a couple of broken branches from the tree's could have been placed over her?
Either way it seems a feeble attempt of concealment.