Just got to wait till it cools down a bit at night and I get my delivery of beans I am putting the two 600s with 4 plants I hope to get a bit more off it. All my other grows have been under 1 600 with 4 plants
You could simply change to an "AIRPOT" thus allowing you to fit more plants on the floor.
You could use 6litre airpots or 15litre airpots. Grow your plants so they finish under 3ft after stretch and with the 6litre airpots you could fit maybe 8 plants under your 1 600w still with 4oz per plant quite easily.
I was getting around 3.5oz per plant with new strains all the time.
Im an ex coco grower. Do you use Trichoderma or mychorhizal fungi in your coco? Beneficials to aid root growth and nutrient uptake.