No problem man, here's a chart about hps lighting and lumens and stuff, I know there's some good threads on riu but I couldn't find the posts, just make sure it's not too hot, it looks like you have a good air cooled system so you should be fine at 12 inches, but just watch them for heat stress and if they are fine you should be good to go.. As you can see on the chart lumens decrease dramatically every inch higher, I would never go less than 12" though because that would reduce the light coverage quite a bit