For the second time Goutor mentions using different size cards for different note types, but doesn't specifically advise for it or provide a reason. Perhaps his advice for consistency and card size applies only to cards of particular types? (p28)

link to: https://hypothes.is/a/XPphjkNZEe2s3i9VV4qt1g

Incidentally he also specifically mentions 7x9" cards here too. How frequently used were these as a standard?