Well in general this could be a good point, but IMO if you totally (!) filtered your acidic Soup then the volume totally does not matter.

No separation between layers is often if the acidic soup is not totally free of tiny particles. After filtering through a half of a cotton shirt (and squeezing it out to get liquid out of it) you will be left with a solution which will separate from Naphtha at any concentration level (ok of course you need to filter again, if you concentrate further after filtration process).