Minimize Modal bottom sheet on flutter to interact with background

I would like to pick up that Question since I am facing the same "problem" or wish. I would like to minimize the ModalBottomSheet so that the user can look up stuff in the background. Like in Mail from iOS, when creating a new email. So far I created a button which sets the state of initialChildsize from the DraggableScrollableSheet:

InkWell(
    onTap: () {
      setState(() {
        double value = 1 - ((MediaQuery.of(context).size.height - 50) / MediaQuery.of(context).size.height);
        if (initialChildSize == 0.9) {
          minChildSize = 0.01;
          initialChildSize = value;
        } else {
          minChildSize = 0.4;
          initialChildSize = 0.9;
        }
      });
    },

From here on I am stuck. As suggested in the other question I would like to set the pointer and barrierColor only if the Sheet is in its minimal position.

How do I access the showModalBottomSheet and Pointer from within the DraggableScrollableSheet? Or is there another solution?

The result should look like this: