You are placing two different buckles, one on each side of the kilt.

Step 1 determines placement of the left-hand buckle (which takes the strap that is attached to underapron).

Step 2 determines placement of the right-hand buckle (which takes the strap that is attached to fringed, top apron).

So in Step 2, you measure from the edge of the top apron, ignoring the fringe.

Hope this helps!