Yeeeah! I just explained this exact thing to another guy yesterday. 4' space the light should be 3' long.
6-12-12-12-6. Each dash is a cob. That seems to be the best way to do it and you did it
Something to think about is the wattage you'll be pumping in there. 12 cobs at 100 watts each realistically calculating useable light it's like having 20 mhydro 300's Ms.T would be getting a raise
.