Advice on power-head placement please

[newreefer_59]

Have 4 6055 Tunze power-heads as shown in photo. Tank is 5' wide X 24 X 24. Just trying to determine the best placement for these to create the optimum flow. Have set the 7095 controller to Interval 2 and the power at mid range. The 3 (high at the back) heads all aim toward the mid-center of the front of the tank and the 4th head is placed to along the back behind the rock (at left in the photo) and on full power.

Also, plan to add some sort of substrate soon. Is areganite (sp?) the way to go?

Many thanks