So I'm not sure if this is officially how to work this but I think I figured out how to trigger the automatic screen rotation. It doesn't work 100% of the time but works most of it. Here's what you do:

Fold the screen down completely so it's in tablet mode. Go to Control Panel and into your Tablet and Pen settings. Set you screen for Primary Portrait. Save that and exit out of Control Panel. Once you "unlock" it and slide it up to Notebook mode, it should switch to Primary Landscape.

Good luck!