Chronic,

Ideally you should have that light only a couple inches from the tops of your plants..
Put you hand where the tops of the plants are.. and lower the light until your hand feels uncomfortable..

With proper airflow you should beable to bring a 400watt hid within an inch or two ofthe tops of your plants..

This is the most important thing you can do.. From the looks of your plants and the light you have.. you need to FLOWER NOW!!

Thanks for letting us help.. its fun to watch your system evolve. There is a lot you can do but it is very very important to keep that light close.. it will drastically effect your BUDS