Oven racks and heating element
Heat transfer is via 


conduction
convection
radiation


You don't have any conduction as you are not touching the heating element  

The top element has direct radiant exposure to the cake so it will crust the top surface.  Can use the top element (broil) to brown meat.  

From the bottom there is radiant energy to the bottom so that will crust the bottom but to a lower extent as it is shielded by the cake pan.  

Convection will provide the most even heat.  

On the third rack use a smaller empty pan or baking stone to shield the second from most of radiant heat from the bottom but not block circulation.  Preheat, cook on second shelf, and only use the bottom element.