'(Dr. Henry)..dozens of plots failed to show any fringe effects'
Henry's book is very good, but it is flawed.
He used D-76 to test FX, which will fail to produce FX unless diluted beyond its usefulness.
Had he tried Rodinal, or drew upon any of Crawley's work, he would have had different results.
Minimal agitation is very useful for inducing FX.
However, the most valuable outcome is the ability to alter
the relationship of the highlights and the shadows, relative to the midtones.
In effect, you can give N- develop to the highlights while maintaining midtone placement,
shadow placement, local contrast and full ISO speed.
My tests and observation over 40 years suggest
that 10 minutes rest periods is the maximum time to can
consistently process 35mm and expect even density.
For 120, 5 minutes, and for 4x5, it depends on how you process.
5 minute cycles seems to be optimum, balancing FX, tonal control, and safety.