You lost me there with that explanation and apparently have a much greater knowledge of water chemistry than I. I asked Jamil this same question several months back and was told that this was a logical assumption. That's not to say that it is the correct assumption.
But if it's wrong, so be it. I am not dissatisfied with my results. So my process remaining consistent is how I am going to replicate these results going forward. So far, I seem to have been able to achieve with water adjustments what I have been seeking to achieve with regard to extraction, flavor, and fermentation. As long as this continues to work for me, I am going to continue to do it, wrong or not. If, at some point, I perceive a problem that I can trace to an improper dilution calculation resulting from inconsistent mineral absorption in the grain, I'll set out to find a solution.