Actually, if 4 plants were grown in perfect conditions one being 3 ft and three being 1 ft then the 3 ft plant would end up giving more yield than the three 1 ft plants. This is because the plant slowly multiplies its yield while its growing in the vegative state. If you grew the 3 ft plant so that the side shoots grew you would more likely have a much higher yield than the three 1 ft plants due to the fact that a big part of the lower part of the plant does not give due to blocked light. I'm just going off theory here I could be completely and a half wrong.