Position sticky: I want sticky frame to fix on top of scrolling frames not below

When I use the new Position Sticky feature in Prototyping, the frame that sticks to the top always sits below the frames that scroll. This doesn’t make sense because the point of sticking a frame is so that it sits on top of all scrolling content.
Do I have to re-order the layers somehow? Do I have to check an extra box to make the frame sit on top of all others?

Thank you