I have two different types of baking sheets, one stainless steel, cost more, from (I think) Williams Sonoma bought years ago, the other from Target, a teflon coated Kitchenaid one that's under $20, fairly new. Using the same batch of cookie dough and same type silpat mats, same everything else, the cookies on the stainless ones end up flatter while the teflon ones end up taller, puffier. They look like two totally different cookies. The flatter ones tastes chewier while the taller ones are cakey. Does anyone know what causes the difference?