The Tessa instructions say to use Velcro® to attach to the board. If it attaches to the front of the 1” thick board, it seems the raw edges would show.
The Velcro® attaches on top of the board. The valance hangs off the edge. You don’t see the Velcro® or shirr tape. If you prefer to have a wider portion for attaching, sew an extra strip of fabric to the top of the valance.