Richard Knoppow wrote:

A lot of chemical processes are not linear...


I suppose data from the sulfide and clearing tests
could both be used to graph fixing time vs concentration.
By contrast a fixer at 1:4 is a heavy syrup while one
at 1:24 is a light. With normal use a fixer becomes loaded
with the halides and the thiosulfate loads with silver. The
syrup becomes heavier. Available free thiosulfate levels
decline and fixing times lengthen.
I'd expect a more concentrated Fresh fix to be quicker
than a more dilute Fresh fix though a graph of concentration
vs time would reveal some very interesting information.
Using the same fix in the same tray or tank for sheet
after sheet or roll after roll is, in my mind, A method of use.
If that were the only method for film developers there would be
no one-shot use of Rodinal, HC-110, Xtol, Beutler's, FX-1 or 2,
and on and on, all often used as one-shot film developers.
Besides, what other very practical way to practice
single tray processing? One shot metered chemistry makes
single tray processing a gas. No loading of the fixer means
skip the stop. Also, the very dilute fix insures archival silver
levels with one fix. DEVELOP, FIX, HCA, all in one tray.
Make BIG prints in a small darkroom. Dan