Hey Hashy....I found about two feet to be a good starting place for anything older than a seedling with my cobs....as they progress you can go a bit closer....some like it some don't. With the seedlings I start around three feet and slowly go down every other day or so. I've had nothing but success with auto cobs. I'm getting a good pound+ from each run of four plants......thats up at least 30% from my old LED. Hope it helps, pal.