Sort of suggests that the thought of using the longer pvc pipe might work. Although the question would be whether or not the plant is in any way stressed from running out of room as it's roots grow downward. Maybe it doesn't make a difference? I would think it has to stress them to some degree. Naturally they want to just continue down, not hit a piece of plastic and be forced back up. Would also solve your sog 'problem' of space. You don't need to make a larger container for them to grow in. Just taller. Course then you run into a height concern. Is your area tall enough to have the plants start out at 2 feet off the grow floor? Just flappin' my lips.