Your calculations are off due to your lack of understanding of the growing methods.
You're going to have 12 plants under 600w. You're only going to have 6 for the first 4 weeks.
To pull 4 oz per plant, youre going to have to veg them for several weeks. And if you veg them for several weeks, you ain't fitting 6 more in there once the originals stretch.
6 plants with 4-8 weeks veg will cover every inch of useable light in a 600w's effective area (around 3' X 3')
Even if you did. The 6 new plants you squeezed in there would only have been growing for 4 weeks max. You'd better be using cuttings because you aint pulling 4 zips per plant 4 weeks from seed. But they wouldn't fit. They would get no light, the whole thing would be a mess and youd end up with mostly airy, light buds that don't sell. If youre lucky, the few colas that were able to get in the light wont be rotted out from botrytis.
A "Sea of Green" is a perpetual method. You focus on low yields from a lot of plants rather than high yields from fewer plants. You cant have both.
If you get 12oz from your first harvest under a 600w, youre doing well. I would plan for 8.
If you want to do a perpetual harvest do 2 plants every 4 weeks. That is doable and you could 4-8oz per harvest. Thats up to a pound a month, which is about 1g/watt and would be impressive and/or lucky for anyone with little experience.
