I'm amazed at how green those plants are with such a powerful growlight. It should be able to cover an area larger than that while keeping the plants in good health. Moving the light closer or adding reflective material to the sides of the enclosure would go a long way towards improving the situation. I don't know why I didn't think to ask this before, but what photoperiod are you using?
I'm curious though, why are you growing the plants in the enclosure?