I have cooked pizzas from Costco and Walmart that turned out OK. Tonight I tried my first Papa Murphy's pizza and the bottom burnt. I cooked the pizza at 425 and removed it from the sheet after 5 minutes. At the 11 minute mark I pulled the pizza from the grill and the bottom was burnt. I also tried their cookies at 375 and the bottom got burnt as well. I did all of the cooking on the bottom shelf. I ready that cooking pizza on an upper rack would be helpful. Any suggestions on how to cook their pizzas?