i just flowered one topped plant that was tied down to 60cm, and if not tied possibly over double in size and got a 3 oz yield. I grow a in box only 900mm x 450mm x 350mm with one 150 metal halide on top and 2x 18w growlux fluros on sides. I start by topping early in veg and do it atleast 6 or 7 times. drill 4mm holes on top edge of pot, and i use those little wire ties covered in plastic that come with freezer bags to tie down to rim of pot. when plant gets taller you might have to join them together at the ends. You just loop 1 end into u shape. Then put that end around the stem you want to tie down then place through drill hole directly below stem, and pull down slowly till the leaves on the crown are facing slightly downwards. The light at the top forces it to grow back towards it,this forming a place to shoot new new growth and make use of a small area.you can then drill screws into side of box and leave hanging out about 35mm so you can tie stems to the end of the screw this forming z shaped buds. be creative and you get some cool looking buds, Trust me. If you snap a stem dont panic coz it will form a knuckle to support itself and will end up being a stronger stem from it anyway. hope this helps.