As it happens, I've just returned from a long weekend on Exmoor. Unfortunately, I can't help you with your query.

I visited the Longstone and some of its surrounding barrows and stone settings on Friday with an archaeologist employed by the Exmoor National Park. I didn't see the stone setting described by Rhiannon, although we did see the quincunx and another nearby stone setting - and failed to find some others.

What I can say is this:

There are more than fifty surviving stone settings on Exmoor and many more have been destroyed. Some form various geometrical shapes - some appear to be randomly placed - and are usually formed from small stones which can be very difficult to find in the moorland vegetation. In preparation for my trip I was surprised to find very little information about these settings. There doesn't seem to be any book or website with diagrams of them all. If I lived locally I'd like to do it myself, but as you know, Exmoor isn't very near to Brum.