Hey Gastanker. Something tells me you don't have the spectral data for those LEDs, do you? If you can find out anything about them, (factory where they came from, model numbers, whatever), maybe we can find the spectral data for them. I was on Mouser.com looking up the spectral data of other white arrays and many were either lousy or very poor for growing. Cree makes some of these I found out and while very bright, the spectrums were way off for growing. You're probably using arrays with very poor efficacy and/or off target spectrums. The red spectrums could be very low in output and are peaking at 650nm, which means you're getting little 660 and almost no 630, and in my opinion that makes it very tough for flowering when using LEDs. You might even have an array that is made of a bunch of blue LEDs that just have a yellow phosphor coated on them which will give you white light, but not at spectrums which are very good for growing, or at least flowering. Who knows maybe it's something else, but that data will help you figure that out. I say all this because to me when I look at those pictures I see plants too small for the wattage and your skill level, so something is off, so I bet it's the LED's ability to flower.
Good Luck Gas and +1 on the UVB idea .