For Best Air Circulation
Hot air must circulate around the pans in the oven for even heat to reach all parts of the oven. This results in better baking.
Place the pans so that one is not directly over the other.
Use only one cookie sheet in the oven at a time for best air circulation.
Use the following as a guide to determine where to place the pans:
Place in the center of the oven rack.
Place in opposite corners of the oven rack or on two separate racks.
Three or Four Pans
Place in opposite corners on each oven rack. Stagger the pans so that no pan is directly over another.