I think experimenting is the way to go. Everybody is just a little different. My standard is 12 oz. It gets out a lot. The more oil, the greater the amount of bile and the more the momentum to get things moving.
I have used 8 oz. and I was disappointed with the results. I don't like to prolong the agony with the additional number of flushes.
Whatever your body and your mind can take is the way to go.
Good luck, Giz.