Zompton, in my time here I don't think anyone has ever asked how to grow a plant taller and lankier to fill a height requirement.

I see your logic, "utilize your space". Do you want your plants 6' tall, or is that where your ceiling is? In a small footprint like you have, maybe the best option would be to separate your space into 2 chambers on top of eachother. You could keep a small cloning space in one?

Trying to get your plant taller is only going to lead to disappointment imho. Your 400w probably has only 2-3 feet of "good penetrating" light under it anyways. You would be just as well served flowering 12" clones and just stuffing your footprint full of em for now. I think you'd be surprised what 10 or 12 small clones will give you versus a couple tall trees. I have run both ways before and while i love looking at a big tree with a huge cola, you still only have about 3' of good growth down from the top. That means that you shift the non used space from the top to the bottom, a moot point if you think about it.

I don't think LST is what you were looking for. While it would help fill your space, you don't have a problem with it getting dense. I think you should look at how YOU are utilizing your space, not how your plants do, and see what you can change there:thumbsup:

Just my thoughts, don't hold em' against me:detective1: