I was led to belive by not only my friend but two local hydro shops that you could only get a yield in respective to the amount of light hence 4 plants are competing for light [under one 400 watt] but its quite possible to get 10oz from 1 plant under 1 light because its not competing for it
when you look at seed packets it gives you a yeild per square meter if 4 plants are taking the same space up as 1 plant they are fighting for space and light