How much fragrance to use in shave soap

[soapkitchen]

I've always calculated fragrance based on the IFRA guidelines and usually use 1oz ppo unless the IFRA is below that. My question is some people add the lye weight along with the oil weight. I make shave soap in small batches and oil weight is between 9-18oz so the amount of fragrance is very low. Would adding the lye weight be allowable?