I agree with growdemon that the lamp arrangement could be a lot better. How about the lamps arranged with the sides of the lamp facing the plants either by putting each lamp vertical to the side of the plants or over the top but positioned horizontally with a reflector of sorts. A flat white surface makes a great reflector. A fan is a must. Try and keep the temperatures under 80ºF day time and above 65ºF at night. With the right nutrition you should be able to pull a good yield with that space and lighting.