AR is width:height.So if you are thinking about an iPad for example, it should be about 3:4. (more tall than wide). For now, we don't have the ability to specify a card to be exact "full screen", but it is on our list as future enhancements.
Similarly, we don't have yet the ability to specify cards that "snap" (stoping at each card). The browse-pages are just smooth scrolling for now.
Layouts are infinitely long, they expand to show all content in the collection.
The layout can have two columns -- and a cell shape (aspect ratio), but a layout does not have a row count and the content shown in a layout floats above the background (no lock).
Margins and top nav can take space too, and will interfere with "entire screen" --
And card design can play a part. If you're using full image for the card, it should be good -- but a card format with image top, left, or right also has an image aspect ratio on the card. So there's an interplay there as well.
Ok I'm still confused. If I have 2 columns and 4 rows and my card is designed to take up 2 columns and 4 rows on a 4:3 aspect ratio on the iPad and my card image is 1024 x 768 at 144 ppi - then why doesn't the card fill up the entire screen?