I can't find it in writing anywhere, but I believe the correct procedure is to lay down 1" tape, rivet thru that, then cover with 3" tape. The 1" tape seemed thicker than normal, and might have been cotton. Parts 2, 4, and 23 on the drawing suggest that same method, but do not depict it clearly.
Edit: 1" under rivets, 3" over is exactly what Joe's picture shows. Can't tell from the photo, but the 1" reinforcing tape that I have previously seen looked considerably beefier than standard dacron tape, and had a different weave.
Edit 2: Spruce sells a "reinforcing tape" for this purpose. FAA approved under the Ceconite process, which uses mostly identical materials to the original factory dacron and dope process. It is polyester twill, not dacron. Narrower than the spec. The current Ceconite process uses Super Seam II cement for adhesive, which is a hell of a lot stronger than dope or the old Super Seam I. It is also reportedly the same stuff as Poly Tak.
Ceconite Reinforcing Tapes (FAA APPROVED) Polyester twill with adhesive back. Applied under rib lacing, pop rivets, or PK screws to prevent fabric from ripping. 60 yd. length.
www.aircraftspruce.com