Can't think of any scientific reason for a cluster...
All are aesthetics or design issues..
Best would be a cluster on a moving arc across the tank simulating a normal sunrise/sunset geometry..
Sun's rays on the ocean are basically perpendicular to the surface at noonish (emulated more by panel than cluster) and the angle changes by rising and falling (emulated more by moving a well collimated cluster)
the "scientific" basis would be catering to the natural geometry of the world..
so the rest is more "cultural and aesthetics"
kind of depends on your definition of "scientific"..