"Are you sure?...
...Makes for a slightly denser neg, but with more shadow separation, since you're getting off the toe of the film curve."
Yes, you are right from a nuts and bolts perspective. I guess I was being more theoretical as far as thought process goes. I used the word "blindly" to really get at what I meant: Blindly downrating your film gives you no *specific* control over shadow tones. I was getting at the fact that if your shadows need more separation, it's because you just need more exposure at your tested EI. Using a lower EI based on box speed alone is a quick and imprecise fix that can more often than not, in the average composition, have bad disadvantages. Shadow tones can be specifically placed anywhere on the curve that you want them by using your working EI at all times, not a guessed EI that you apply like a blanket in all situations. Simply downrating your film, using your meter as normal, and processing as normal will give you a flatter neg (assuming there is a normal range of brightnesses in the composition). Remember that there is a shoulder at the top too...and it is generally longer than the toe. Therefore, in a full-ranged scene, if you overexpose, you lose more highlight separation than you gain in shadow separation.
In short, I was arguing against generalization, and for specificity. But, yes, you are absolutely right about moving stuff up off the curve increasing tonal separation *in the least dense areas of the neg.*
