OK - usually I smoke two racks at a time and use the top two racks. Needing to smoke at least three racks and not sure if I can use the lower rack nearest the heat element without overcooking/burning the ribs. If I should not use the lower rack, can I stack racks of ribs on top of each other on the top two racks? When you increase the amount of meat does that increase the smoke time or is it 225 for 5+hours still. Thanks for help with this rookie question.