The shape of the opening of the runners is very important. It seems counterintuitive but looking at the number 5 and 6 runner openings you will see how the divider at the floor is hooking away from 7 and 8 and towards 5 and 6. You need to move the bottom of the divider out of the way. And shorten it up at the bottom. I would also lay the outside wall of 7 and 8 where they open into the plenum back some. You have to make sure you don’t break through there. Even if you do, it can be easily welded. I don’t remember how much materiel you have to work there. And yes on the area.
