If you prune SoG style, removing all branching from the lower 1/3 of the plant, you can conceivably do as many as 4 per sq ft. SoG plants eliminate the small, fluffy popcorn buds produced on lower branches, instead producing the big nugs on the top cola and the golfballs just below, attached to the mainstem.
Sea of Green ops also keep plants short by flowering clones immediately after they have set root- no veg time between rooting and flowering. Short plants are the indoor growers' friend as even the mighty 1000HPS can only penetrate foliage so deeply.