Most conventional ovens have heating elements on the top and bottom of the oven but tend to get hotter and cook food faster on the top rack. Hot air rises within the oven cavity to create a hotspot at the top of the oven, so it may be best to place dishes requiring longer cooking times on the top rack when multiple dishes are competing for oven space at once. This is less of a concern when using a convection setting which helps circulate air for more even cooking from rack to rack.