I set mine up with gate valves going into the fuge section, so that I can control how much I want going in there and divert everything else into the skimmer area of my sump. I still tweak it from time to time too. I don't think %'s are really the best way to define this, moreso in terms of GPH
. I run a 700GPH return pump in my tank, and of this I try to limit my fuge to about 100-200GPH and the rest through the sump. No specific reason for why I chose 100-200, that's just where I *think* it should be.