Yes, John, that is correct. Typically the manufacturers ISO rating on a film is based upon the zone I density being .10 above FB+fog. Thus the sunny F16 rule would follow the manufacturers ISO rating. I find that increasing exposure above the advertised ISO (in this case derating FP4 by one stop) will impart better shadow separation (by getting the exposure up off the toe of the characteristic curve sooner).
Originally Posted by John McCallum
The additional benefit is an increased sense of light within the image. This is all true for exposures without a meter. If one learns to read the intensity and quality of light without the constraints of a meter that leaves more room for intuitive photography in my opinion.