The chloroplast for my cages covers 3 holes in the grid.
I also have chloroplast behind the hay rack. I use S hooks to hang the rack on. The chloroplast is on the inside of the cage so hay can't get caught between the grid and the chloroplast. The S hooks and through holes and hooked onto the grid bars for stability. This seems to keep most of the hay in the cage and not behind it.
I use poster hangers over the edge of the chloroplast to prevent chewing. Penelope will chew the side right down, but can't with the hangers on. When you put them on, you have to slide them, so it is best to do it when you first build it. They come in 2ft lengths and usually 2 in a pack. You will probably need 3-4 packs depending on your cage size.