I have similar questions, Bill. Still working on these tests and it will be a few weeks yet. Lots of data to go through. I've used localized and/or masked pre-flashing fairly often with extremely high contrast subjects, and always did it the way I was taught and the way it made most sense to me, but I've always wanted to do a rigorous "study" on it to hopefully answer some of the nagging questions I've had. Pre vs post is one of them, but the one I've had the most trouble getting my head around abstractly is what effect there might be (if any) if the flash exposure on VC paper is done with different filters. The conventional approach is to simply flash with white light, but I wanted to investigate this further. Another one of those rat holes I guess. The procedure works fine for me as-is, but who knows, maybe there are additional controls, or maybe a myth or two can be busted. There is little written about it, and no real evidence for any assertions. The exception is Henry's book - but that was with graded papers. So I kind of see this experiment as a continuation of his work but with VC papers.
Michael, with all due respect the tests you are trying to do including filter values, exploit so many variables that they become almost meaningless. From a physics point of view I find it difficult to believe that a pre-flash has the same effect as post flash. After exposure the latent image is at a variation of energy states across the entire shadow to highlight range. How can a post flash possibly give the same values as a pre-flash where the exposure value is zero and even before exposure to the variance of the image in question?