I perhaps should have qualified my statement a little more by adding that it is going to depend on the number of ingredients and amounts thereof. I use 6 ingredients; if I round down what SoapCalc says for a 64oz batch, I lose 3 oz of oils/butters, but depending on my percentages, I could lose almost 6 oz. For my particular combination of oils at 33% Lye Concentration, my water is 18.52, my Lye is 9.12 (2% SuperFat).I disagree with you on the rounding down being an issue.
For the last two years the importance of accurate measurements has been drilled into my head, along with using a single soap calculator. Now you are basically saying that because SAP numbers are a 'range' and no one has pure lye, close is good enough. I'm sorry, but I can't agree with that...not with something that is going to be used on my face, my lady bits and my grandchildren.