Got my new 15x15 clamshell heat press this week. Gonna use it for the first time today. I can't find much info on it. My only question is the thick black pad that's in it. What's that for? It was stuck to the top platen originally, but I noticed it fell off. Is it supposed to be on the top? I'm thinking it was just stuck there and it's supposed to be on the bottom and that's what you set the shirt on. I just want to be sure. Thanks