cheers mate is there anthing i can do to get better yield using that kind of light
everything is relative, think of it as a maths equation.
the factors to consider
type of plant you want to grow, sativa or indica
how you want them to grow, you can get 20 plants in the same space as 10, if you don't let them do side branching. If your just growing the cola then you can have them much closer under the light, so you get less per plant but then more plants.
If you want less plants but the same yield, then you have to veg them for longer and promote side growth and give them a little bit more space. but then you have to factor in the time to achieve this.
You can't break the laws of physics so its nothing more than maths to figure out how to improve.
what I would do if i were you, would be to have the lamps in a square formation, increase the gaps between them because there will be a slight overlap of the lamps which will give you more coverage allowing either more plants in or less but much bigger plants in.