Light that goes straight down will cast larger shadows? I would think a single light source (i.e. a Lumia) would create larger shadows as a wider beam since everything in the light of sight will shade things. Which IMO is one of the largest issues with many of the current LED setups, they have clusters to reduce color banding, but then that tends to make a single light source, even when you get things like the Radion setup, you get 2 light sources, compare this to a T5 setup which might have a 2-4 foot long light source that's a few inches thick, or a metal halide that could have a as large as a 19" x 19" light source with the largest of reflectors.
Someone really needs to make a setup that moves their LEDs across the tank like people do with metal halides