I ran a roll of TMY2 batch 0167 through D-76. The curves (using two lenses):
There's a small inflection at X=-1.4. That also is the location of the transition between the lower and upper rows of the Stouffer step-wedge, suggesting the problem is uneven illumination. But curves for other films look fine, with no inflection there, so maybe that's just a coincidence. It's hard for me to say, and I'm going to change illumination to hopefully insure uniformity by adding more diffusion.
On a different topic, I plan to reduce both metaborate and ascorbic acid in D316 to see what effect that has on the toe. Some similar experiments I did a few months ago look encouraging.
Michael R: If you re-measure Acros, could you post the curve? Or maybe post the numbers and I can plot them using gnuplot and will post that. Thanks!