to me this video is a great example of when somethings not working try something else. I was working with a horse who insisted on doing this backup by going sideways / diagonally. I grabbed my carrot stick to help keep him straight. Worked within 3 goes.
But it did work. If you look on the tape in the first 20 sec the horse backed up 3 different times and the handler never released pressure. The horse did it correctly but was never told he did the right thing, from there it went down hill, the horse just guessing as to what was wanted and no clear signals ever given.