You really need to decide how you are going to aquascape your tank. I have seen one VERY successful tank that had the returns in each front corner with a 45 degree "T" so it was going across the front from each corner and towards the back along the sides. That, coupled with his returns made for nice flow. He is considered the SPS "king" around here.
What I did was create a "vortech" of flow - since mine is a peninsula - starting with the returns going down from the end - as well as across the top along the sides - then the closed loop's first return (split so it goes on each side of the center rock) goes along the bottom towards the second return which goes upward toward the end of the tank and then the MP20 along the top facing back toward the overflow. So it creates a circular vortech of flow around the whole tank. It takes a little while for it to stop once the pumps are all off. I have zero dead spots and very happy corals.