public void setDragScrollStart(float heightFraction) {
        setDragScrollStarts(heightFraction, heightFraction);
    }
Set the width of each drag scroll region by specifying
a fraction of the ListView height.

@param heightFraction Fraction of ListView height. Capped at
0.5f.
third_party/DragSortListView/src/com/mobeta/android/dslv/DragSortListView.java