Your approach seems sound, but conservative. If you look at the moment contours (or deflection contours) I think you will see a fairly traditional behavior a few feet from the wall supported edge. By setting up your design strips with "Design Column Strip for Column + Middle Strip Resultants" you are penalizing the column strip for the whole length, when really it is only the area near the edge that is a concern.
If that's right, and it's only at the edges where you want to consolidate the rebar you could taper the design strips, something like this.
