Group Focus ABOVE reference element? Drop-down menu expanding upwards?

I am working on a native mobile app with all the navigation elements in the footer. I’d like to use drop-down menus and group focuses, but I can’t figure out how to get them to expand upwards instead of downwards. I also can’t figure out how to get the group focus to anchor above the element instead of below, and the offset only works when the element doesn’t change size.