My methods are based on sound Spherical Trigonometry applied to a Spherical Triangle, in this case the Earth. The equation in my above post is derived from the Cosine Formula. Essentially what it is saying is that if the declination of the Sun is negative (Southern Hemisphere summer) the azimuth of Sunset is between 270 degrees and 360 degrees, ie North of West. If the declination is positive (Southern Hemisphere winter) the azimuth of Sunset is between 180 degrees and 270 degrees, ie South of West. The value of the Sun's hour angle at setting for a given latitude is dependant upon the Sun's declination.
Dan