Baldy.....I use 8 x 4x 8. I grow hydro. I've been getting about 4-5 oz with 4-6 plants in the space. That's 4-5 oz per plant...not total. I use a 1kw light. Everyone can add the numbers up any way they want and hash over watts per...in my HUMBLE opinion you have enough light and that's not your problem. if you have enough air space per plant then check your soil space....how big are you pots? And if that isn't the problem I'd start looking at your nutes and ph etc....just as HTID said above.

I've crabbed out my piece so will now leave you guys to decide.....Good Luck