You got some good answers. Just my opion.

If you put 12 or if you put 2 in the space will yeild close to the same. Yes spaced out plants get more to the bottom while close has more tops.

Now what it sounds like your descibing is a screen of green. To get max yeild in a small place. A screen with 3 to 4 inch holes are placed over a good number of plant at about 12 inches high. A standing cage. Veg them and wieve branches through the screen. When they flower you have many buds about the same size.

What they busted me with was a true sea of green. I had 10 gallon containers with 6 plants in each one. 5 all toghether. I had a mother/clone room, a veg room and a flower room. 6 plants go into flower, one month later 6 more plants go in to flower and so on. In the stages of clone and veg are 3 more containers of 6 plants. Each month I would harvest betwen 12 and 16 oz's. Well once you get here it's gavy but a lot of work to get there.
Just thought I throw in the sea of green story. Watch your back. Tell no one. My Nephew got me.