The feedback I received from our eBound/Benetech review suggested that
Best Practice: Attributes Placement
SMART GCA: (General Accessibility) 4.11 Attributes Placement
epub:type shouldn’t be captured in <body> element where there exists an equivalent role, except in the case of <body epub:type=”bodymatter”> Observation
The cover image xhtml page captures epub:type in <body> element instead of in element.
But after some research it appears that w3g considers “cover” to be a document partition:
A section that introduces the work, often consisting of a marketing image, the title, author, and publisher, and select quotes and reviews.