Raw unskimmed/filtered water is where the highest accumulation of nutrients is going to be, which is what feeds the algae in your fuge. This isn't to say that there aren't still nutrients in the left over water coming from the return, but to maximize the benefit of growing macro, you want it consuming as much as possible. The way I have always plumbed my fuges is to tee off of the inlet to the sump, or down pipe if you will, so I get raw water. Then the return from my fuge dumps back into the sump before my skimmer zone at the sump inlet as well. Like I said, if it were my sump, I would suspend a small fuge over the top of the return zone wit either a pvc platform, or something to that effect.