I do recall seeing something by Maddocks in the 1930s that R/R1s weren't considered high-capacity cars for mass movements because of their more restricted loading provision than the cross benches. Maddocks must have been the last person in NSW transport history (at least until the advent of the metro) to be acutely aware of the issue of capacity. He was forever banging on about it during the growing contemplation of replacement with buses. Post-Maddocks it became an inconvenient fact to be ignored. The R/R1s had close to the capacity of the cross benches but were a little slower to exchange passengers.
On that last note, yes Maclean referenced the Brisbane dropcentre as I said, but what interested him most about it was the ability to also exchange passengers through the ends of the car as well as the centre (the Brisbane cars originally had open platforms at the ends before the cabs were enclosed). This car was the most direct prototype of the R and overcame the problems of the "cave", the dead end saloons in the Adelaide and Melbourne cars.