The returns are on the overflow side. I'm never a fan of high turnover and close loop system. 3x turnover is about max that I would run on a tank.
The flow was quite a headache for me for the past 3 weeks. While trying to avoid a pump on the other end of the peninsula, the two 6255s on one side was either too much flow in some area and not the others. Sand devils under the pumps, craters in the sand. LPS flesh pealing because it's being dragged by the strong undertow while SPS polyps at the top of the tank are at a stand still. I was ready to pull the trigger on 4 MP60s, two on each side. But thought why am I doing that when I can try to place one of the Tunze on the other side if I'm going to put a pump on the other side anyways.
I did that and the flow is much much better.
In the end, it's about the critters' health and response that matters. Not what you fantasize on how your tank would look.
Any tank that is more than 6' long would have a real problem with flow without a pump on the other end.