I've made these a few times and LOVE them (big hit at the Super Bowl party last night).
Every time I've made them, they come out flatter than the picture.
BUT, last night, ONE of my sheets (I doubled the recipe, so I had 4 sheets) came out just like the picture. I don't know why, but I do know this was when I used my thickest, heaviest cookie sheet. Maybe it's about how much heat the sheet retains. I'm not sure.