I just reread Sandy's very well written article on unblinking eye about UV light sources. I have a question followed by a rather lengthy explanation behind the formation of the question, please bear with me.
I noticed that the HID lighting set up you illustrated was positioned with the bulb in the verticle position. And you talk about the light quickly falling off at the edges. You placed the light 20 inches from the surface in order to cover, I think it was 11x14. Are you aware that there is a difference in HID bulb mounting? There are those that were designed to be screwed into your lightsource in a verticle position and there are those that are meant to be mounted horizontally? If you were, did you try both? and if you did, did you notice any difference in the evenness of illumination?
In the field of hydroponics it has been known for a long time that the horizontally mounted bulb is much more efficient because it provides a much more even illumination over the garden area. In my classroom I run two horizontally mounted 1000watt fixtures. One is a Metal Halide and the other is an AgroSun bulb designed to mimic sunlight. The illumination of these two bulbs are very even. If you are still running the HID unit you might want to expore the horizontal mount, though you would need to replace the reflector. I have Tested a verticle lamp on my gardens and found it to have a serious hot spot with quick light fall off. I do not have that problem at all with the horizontally mounted bulbs.
I must say that your article was very well written and this thought popped in my head.