This is my first post!
I had a question regarding hnefatafl and I though this would be a good place to ask the experts

I recently picked up a copy of hnefatafl from the Museum in Edinburgh and have really enjoyed playing it.
After googling (a lot) I found the Carl Linnaeus tablut rules which seem to work nicely (for me at least) though I've still been using a corner escape for the king.
However, this led me to the following question:
I was wondering if anyone knows of any historical evidence for an 11 x 11 board? and specifically one with corners marked? I know, there has been some evidence for corner marked 7x7 boards (The Balinderry board) but I'm struggling to find any 11 x 11 boards other than the Trondheim one (which seems to have different markings).
I've seen the Ockelbo Picture Stone as evidence but the quality is unclear, for all I know it could be showing the initial placements of 5 groups of pieces....
Any help/insights on this matter would be much appreciated.
Cheers
Kev