I've noticed that I tend to end up with about a 1/2 gallon less post boil volume than Beersmith gives me in an 11 gallon batch. Whether it is from too vigorous of a boil or evaporative rate I can't say, but it is fairly consistent.
I changed the boil off rate from 1.25 gals to 1.75 gals and have "Use boil off as an hourly rate" and " Calculate boil volume Automatically" checked. I expected to see an increase in my recipes of sparge water or pre-boil volume but saw a decrease instead. Should I then return the boil off rate to 1.25 and increase the boil volume by .5 gal. or how would go about getting this resolved.