Apologies if this takes the discussion off course, but one thing I think of from time to time is the concentration of flavor-perception ions in the wort (sodium, chloride, sulfate) as we boil.
We use these calculators to designate a profile we want for the mash ... but then after the mash we boil anywhere from 30 minutes to 90 minutes. Can we assume that the concentration of sodium, chloride and sulfate will be appreciably higher in the end product when undergoing at 90 minute boil vs. a 30 minute boil (or no boil!) ? I've looked for boil impact info on water chemistry and have come up empty.
And wouldn't this be even more impactful in a small batch of, say, 3 gallons; if we start with 4 gallons of wort and boil off a gallon to finish with 3, are we not increasing the concentration of these ions by 33%? (xx ppm @ 4 gallons = xx*1.33 at 3 gallons).
Does this even matter??