Apple emphasises the “Transparent book cover” effect when demonstrating Duo. This works well when the cover view is detail as in the HIG Duo Best Practices section example with an email. But if the cover is showing the list and the Duo is opened then the choice is:
a) show list trailing (transparent cover) - perhaps transitioning to leading when an item is selected so that the detail is primary, or
b) show the list leading (abandoning the transparent cover but classic pattern immediately )
Which is recommended?