Since several unknown compounds found even in essential oils accelerate or inhibit saponification, each batch type should be tested if you want predictable results. These percentages are out of the entire weight of substances used in a batch of soap including the fats, lye water, perfume color etc. I use a large veterinary syringe to meter the correct amount of DPG into the soap batch. Essential oils are just one form of natural concentrated scent. Many natural scented oils cannot be steam distilled due to insolubility in steam or sensitivity to heat and must be extracted in some other way.
Many natural fragrances are liable to saponification and can only be used in re-melt.
Unfortunately, you can only find out about these by the sad experience of having no remaining scent in a cured batch of soap. It is best to make a recombinant oil from natural scented fractions vacuum distilled from natural sources, as many synthetic fragrant compounds have contaminants from synthesis that cannot be cheaply removed. That is why many perfumes smell off or cause bad reactions. As already mentioned, it causes soap to trace quickly and is good for the skin. It is best to purchase fragrance oils for soaps from a reputable soap-makers supply company.