The taking edge of the ribs need trimmed to match the RS-15 taking edge piece. They also need to be trimmed to the same length.
The RS-15 is an odd shaped piece, using a piece of RS-15 scrap I measured the angle that the ribs need set to, a whole 2 degrees. Setup my guide on the sander to this angle.
Next I cut an RS-1 to act as a stop so I can easily sand all ribs to the same depth. I clamped a piece of plywood to the front of the rib, note that it is necessary to tell trim the horizontal RS-1 flush with the vertically RS-1 on the front of the ribs first.
Now I clamped the RS-1 stop piece to the rib placing it flush with the plywood piece.
Then I held the bottom of the rib flush with the guide and sanded until the RS-1 stop stick hit the guide.
They may not all be exactly perfect but they are close enough for as fast as this bird will fly.