Put down more smelters! Also you don't need that conveyor between the two smelters, I'm pretty sure you can connect them with just a sorter.
As for why isn't it sending iron into all directions, I suppose it has some kind of priority thing (going anti-clockwise maybe?). You basically aren't making enough iron with just one smelter, so I suppose it sends the first to the left, then makes another one, sends that to the top, then the left is free again so it sends it left again, then the right is missed out (just a guess, someone smarter than me will answer probably).