i would argue larger holes would have less cooling. less thermal mass to spread the heat away from the cage. this is why my covers have more material on the sides where the screws connect it to the cage.
At the risk of starting a Mech E discussion, that's not the intent of the cover. It was to keep fingers out, EMI in (likely?) and to allow some air flow to cool components. It was not designed to dissipate heat through conduction.




