my best advise would be to find what works for you. by mixing soil and soiless mixes yourself, you are trying to acheive an ideal growing medium for what ever your growing. cannabis happens to like a loose, airy, drainable soil. perlite and vermiculite added will help with drainage and aeroate the roots. alowing your soil to dry a lil between waterings. most people dont use more the 33% in there mix because and more and you have to water more frequently. i use prolly a 40% mix cause i use oceanforest AND am a cheap bastard as perlite is cheaper then the soil. i dont mind having to watermore often. i think the roots like it! like i said, what best works for you. every strain and enviroment is different and that has a major factor in determining your mix!