i think you're talking about rails similar to an aeroflow unit? if so, i run 6 plants in a 5' rail, plants 8'' center to center. i veg for two weeks, or to 10-12'' then flower. my indi's end up about 24-28'' tall, 2oz each average, sativas get about 30-36'', about 12oz per 6 plants (close, but...