Yeah... I'd go along with all of that, and especially like the 'peeping effect' idea.

There's just one tiny fly in the ointment though when it comes to the number of places Silbury can be seen from - trees. Four and a half thousand years ago the area may have been far more wooded than it is today and that would probably have blocked out some modern views of Silbury.

There's an example of tree-blocking actually; about a quarter of a mile down the road from Winerbourne Monkton, heading into Avebury, Silbury is just visible through the trees in wintertime. Once the trees have their foliage you can't see it (though I've never actually stopped the car at that point in the summer and checked the view carefully). There maybe other places where Silbury is only visible when the trees are bare.