Re-looked at the map and there's 3 dots, 2 for bullauns and 1 for the cross-base. The stone in the foreground here was the one I thought as possible. It's only a possible as the stone looks earthfast and the bullaun/indentation is horizontal.

BTW. Muff = (a corruption of) magh = a plain: arrived at by the usual scientific approach that certain elements used here in the past. ;-)