Whenever I see a switch used, it always takes me back to the ferocious whippings my Mum gave me for the slightest of reasons. Usually on the bare bottom, sometimes on the backs of the legs, always with the buds left on to ensure that the pain was excruciating.
Not sure about that one, I think either bent over or at least bottom raised is best for the birch not to mention a decent number of twigs bound together.