Ballinderry, Ireland, late 9th century

Modern reconstruction of the Orkney board (Antiquity Gamecrafters):

Although the Irish and the Orkney boards are both of size 7x7, they are clearly different in the markings. The Irish board has marked corner squares, whereas the Orkney board has no markings of corners.
We know that the Historical Hnefatafl rules are well balanced on the 9x9 board with no marked corner squares (Saami Tablut). But reducing the board size to 7x7 would make the Saami game very unbalanced in favour of the defenders. To rectify this, the king can be required to go to a corner instead of the edge, and then the game is balanced again (Irish Brandubh).
An alternative way to rectify the balance is to drop the throne square and with it the special protection of the king in center. Then the king still wins on the edge, and the corners are still unmarked.
We tournament tested this setup and found a good game balance of +1.11 (111 defenders' wins per 100 attackers' wins).

Could this be the ancient Scottish game played on the Orkney board, i.e. the Scottish Ard Ri: Historical Hnefatafl rules but with no throne?