I re-read Whittles 1991 Antiquity paper last night and have nothing further to add to the knowlege of Silbaby but Whittles comments are interesting and reflect other views expressed here.

"To have missed one enclosure so near to other major monuments may have been bad luck, but to miss two begins to look like carelessness".

"The full extent of the archaeological records in this flagship area are not known, simply because we have not systematically examined them".