You can lay a rack flat on a 18" but the ends are at the edge of the grate and they get really dry. If you put three racks on an 18", one goes down the middle and the two on the outer edges have to curve and the grate is basically filled with meat. Again, the meat around the outer edges of the grate gets too dry. I've done this one time and did not like the results. I use to cut the racks in half and use a rib rack, but that means I have to clean a rib rack - not fun. The results were good but I'm adverse to additional cleaning work. So now I roll them as shown above and I really like it. No additional clean up. Just throw the skewers away. Works great. Bottom line is that if you want to lay ribs flat, you're going to have to get the 22" in my opinion.