Placement of Powerheads

[Blue Ram]

I've ordered another Tunze Turbelle 6125 for my 120 gal reef to increase circulation as I am getting some red cyano setting on the rock/coral and sand. Most of my rock and coral sits in the lower half of the tank.
I will now have 2 Tunze 6125 and 1 large hydor powerhead. The tank is 4' 120 gal with a large overflow on one end and two outlets at the other end. What would be the best placement for the powerheads to provide an even amount of flow throughout the tank and avoid areas of no flow?