.........To faciliate lining up the cuts, I attached a small piece of scrap in line as an extension of the MFT fence, then ran the router bit into that fence. After that, all I had to do was line up the outside line of the dado with an outside edge of my cut through on the auxiliary fence extension. (This assumes the reference edge of the workpiece is straight and is kept parallel against the fence throughout, and I checked both ends of the line marking the dado relative to the guide rail before making the dado.)
Dave R.