I also run two Orphek PR156w's and had a similar issue with shadowing on the fish and the corals around the sides of the tank... before anyone slates the lights i had the same issue when i ran a halide with inbuilt T5's.

To overcome it i now run a couple T5's either side of the tank (my tank is viewable on 3 sides), this sorts out the issue. I think it would be that same whatever LED or halide i were to run as they are all a 'pin' light source so will shadow anything as soon as its on the outer edges of the light spread.

HTH