Currently the adapter does not distinguish between interior elements and overlap/ghost elements when it defines vertices as coupling vertices in preCICE. It simply passes the coordinates that the user provides. In precice/tutorials#663 the macro-dumux participant code ensures that only interior elements are used while setting vertices and passing data to and from preCICE. Although the application code has handled this for now, it would be more appropriate to handle this in the adapter in a more general way.