Just took time out for an interesting exercise, as someone might do the same. The Isle of Bute at about 122 square kilometre (or perhaps kilometres square) would fit over the Grizedale and Furness Fells.
Therefore Coniston should perhaps be leading and involving at least their fellow towns and villages (and their occupants) which would include Skelwith Bridge, Ambleside, Windermere, Staveley, Newby Bridge, Spark Bridge, Penny Bridge, Blawith, Torver as well as Hawkshead, Near Sawrey, and high Nibthwaite.
If the Proving Trial is going to be bigger than the crew training on Loch Fad, then expanding the area for Cumbria that should/could support the Heritage Event and the Proving Trial (and put concerted pressure on the LDNPA) could extend west to the coast; south to Isle of Walney; east to the M6 motorway; north to Penrith/Carlisle/Wigton/Maryport. In other words the WHOLE of the area known that is known as the Lake District National Park!
[Maybe the hot weather is getting to me!]