I don't know about the yield, I will let someone else help with that question. But, I tried 9 per square foot and hated it. You can't find the beans within that mess of greenery. That was a real pain. And when the aphids attacked, it was almost impossible to get rid of them. The max I would plant is 4 per square foot. I now do about 2 per square foot to make it easier to harvest and water and just take care of the plants. Actually I plant them with 6 inches between plants in all directions.

Ya I know the feeling. I'm doing 3x3 in a roughly 1'x1'. Aphids would be not that bad. Scorch it and then replant. Beans are fast.

depends to some degree on the type beans, snap vs shelly vs dry. I would try for 3 plants per square foot with snap beans and 4 per ft with shelly or dry. Pole beans need more room, max 2 per square foot for most varieties I grow.

Ya. Frankly I'm more into killing the slow to germinate beans than the beans now anyway. Evolution!

I have a 4.5' wide bed. I grow 3 rows of bush beans, with each plant from 6" to 8" apart. I never want to plant 4 rows or more since it is not possible to reach the beans from either side. And it is impossible to step into the bed.

It is very hard to pick if beans are planted too dense.

I'm kinda over beans now.