True, you do have to take hight in account.I think it depends on what you can fit in your room. If you flower at 6 inches it will finish at about 12 (depending on strain and if it is more indica or sativa) if you flower at 2 feet maybe finish at 4 feet. You don't want to veg to 2 feet in a room that is only 3 or 4 feet tall..