I agree that the FO/EO doesn't affect the base oils mixture of your soap.
You sometimes may want to compensate the actual scent if you used
a TON of non-deodorized cocoa butter but in a balanced recipe not
that much choco smell comes through.
Usage amounts of FOs and EOs depend on if you HP or CP and
the general strength of the scent in question. You are your own
best judge of stength.
I agree that usuage levels do usually fall between .5 to 1 oz per pound
of oils.
There are several standards that Perfumers and European
Bath & Body makers must follow to comply with their laws
and the standards that are given for the EOs are a great
base line to go with along with your Supplier's suggested
usage rate for whatever application you are using.
IFRA is the International Fragrance Association
http://www.ifraorg.org/
An EU PDF for Regs
http://webarchive.nationalarchives.gov. ... e25422.pdf