Yes, this is a very confusing topic. I like soap with a lot of scent but I also want to be safe. The IFRA guidelines may not be perfect, or even accurate, but they are some sort of a guide for a substance that can be irritating to the skin. I assume that IFRA is basing the usage rate on the total amount of the thing being produced, i.e. total soap recipe. But since I don't know for sure, I tend to try and find FO's with minimum rates of 9%. If FO has an IRFA usage rate of 9% or more, I use FO at the rate of 6% of the total recipe. So for a 94 oz. total of oils, lye & liquid, I would use 5.64 oz. (6% of 94 oz.). But if the IFRA rate is only 6% (about 1 oz./lb. of oil) I would only use 3.8 oz. FO because 5.64 oz. would be 8.8% of oils, which would exceed the IRFA of 6% for that particular FO. I may be being overly cautious, but it makes me feel better.