When I bought my 118 it came with two upper tops both are in really good shape and both seem to be identical. Now at the time I didn’t think about but now I’m wondering why do I have two tops? I’ve notice that although they look the same from the outside they are different on the inside. So now I’m wondering what is the purpose in this? Ones flat on the inside while the other has ridges. Is one made for cooking on top of? It’s had me wondering all day.