I didn't want the cover to be any bigger than necessary, so I made the opening square to allow a tighter fit around the square button on this Fractal Design case.
Printed at 75% it's a perfect fit.
In this case, the offending kitty is Byron and he's been turning off my son's PC. Us old folks know better than to get a case with buttons and ports on the top. :-)
The author remixed this model.
Remixed with a square opening to allow scaling down.