He's also on the back of Spidey on far right, just lower than the middle. At least Namor's head is there.
I was thinking that there's a third appearance on that collage, but I don't see it right now.
Well, of course, WE think Namor should have a bigger more central place. ;p But heck, look how they treated the FF on this piece. I think they were relegated to only the wedding pic! And the Thing looks like he only has an arm showing.