How to translate screen coordinates to group coordinates?

I have some objects that are nested inside of a group. The group is scaled to fit the screen when the device is rotated. You can drag the objects, which works, but the movement is not quite in sync, since the group coordinate space has been scaled. 
 
I’m guessing I’d use:
 
 object:contentToLocal( xContent, yContent )

The reference point of the stage is the upper left, the group positions the reference point in the center. So I’m guessing I probably need to offset this to match? 

Looking for any good ideas or suggestions.