Thanks for the additional replies. There were two important lessons I learnt from this thread.

1. It is up to the photographer to place "darker" colours on lower zones, lest they be rendered the same shade as "lighter" colours.
2. Light meters, panchromatic film and our eyes all have different spectral sensitivity curves. Refer to the following excerpt from p.190 of WBM Ed.2, Copyright 2011 Ralph W. Lambrecht, Chris Woodhouse (I'm satisfied I followed the "fair use" rules).