i seem to remember that in that cris cross setup of heaths the lights were not always on. the middle light was always on, while one leg of the "X" was on for the first six hrs and the other leg was on for the last six hrs. therefore, each plant was flowered using (2)300w(6hrs of 600), plus 600w/2 plants = (2x300)+(600/2) or 900 watts per plant. just like if you throw 2 plants under 1000w, you do 1000/2. you wouldnt say that both plants used 1000w, like agent smith is tryin to say with the middle light in heaths grows.