You could put 60 degree lenses on the LEDs, and raise the light higher. That would give you much more even light intensity top to bottom in the tank.
I do have 60 degree optics, but haven't decided yet whether to use them. I don't want to raise the light fixture much higher than it is right now. From a design viewpoint (as opposed to a plant happiness viewpoint), 9" above the tank is about right. Most importantly, at this height the wood frame blocks the direct glare from the LEDs unless you bend down and look up. If I were to move it higher, the light would be distracting. And the fixture is already high enough that it doesn't obscure one's view of the entire open top of the tank--that was a major design criterion.
In any case, this is one of the best looking DIY stand and light combinations I have seen here.
Thanks (and thanks to all others who posted nice words). It's been a lot of work, and I didn't have the skills to do it before I started. This is my first cabinet of any kind.
I'm now sort of terrified to actually plant this tank and get it going. I am good with a table saw, but still learning how to use fertilizers, CO2 and so on. Fortunately, there's still some DIY bits to procrastinate on--I need to enclose my driver/dimmer/wiring rat's nest, and put some finishing touches on the stand interior.