Sorry I've neglected this series, these covers just never interested me much and I can't find any resources for these films either. I'm going to try to finish up this series soon though.

As for the size, here is the case for this size:
8-DISC/12-DISC ACE CASE 'EDGE-LOCK' DVD BOX DETAILS

Maybe not the best choice but the # of discs varies from each season so I wanted something uniform that would look the same and hold the discs the same (no trays left empty) regardless of how many discs there were.