  For a branched locally isometric covering of metric spaces with intrinsic
metrics, it is proved that the Steiner ratio of the base is not less than the
Steiner ratio of the total space of the covering. As applications, it is shown
that the Steiner ratio of the surface of an isosceles tetrahedron is equal to
the Steiner ratio of the Euclidean plane, and that the Steiner ratio of a flat
cone with angle of $2\pi/k$ at its vertex is also equal to the Steiner ratio of
the Euclidean plane.
