I also have the Addey book and read it from cover to cover and back again. It's based on the modern view of aspects which is that they are the angular separation resulting from dividing the circle of 360 degrees by successive integers (2,3,4,5,6,7... no matter how silly the answer). This has largely been the view since Kepler introduced the so called minor aspects.
Originally things were different. The inventors of Horoscopic Astrology based the aspect on Optical theory as it stood at the time and identified but seven aspects, relating to the seven rays. (one opposition, two squares, two trines and two sextiles).
The very word 'aspect' involves being able to see or view something. Thus the 150 degree separation was originally treated as being something that could not be seen or was 'in aversion' to the viewer. Now it's called a quincunx but means the same thing - in original aspect theory the quincunx is an oxymoron (but note; not meaningless at all).
Clearly some of the 'harmonics' apply to both definitions ... the second, third, fourth and fifth correspond to opposition, trine, square and sextile. However there is no conceptual difference between a square to the left or a square to the right in modern theory, though it used to be a very important distinction, used in identifying the dominant planet in an aspect.
The harmonic approach also produces aspects with very little separation in angular terms and begs the question of whether such distinctions are meaningful. What is the real difference between angles of 40, 45, 51.43, 60, 72 and 90 degrees (division by 9,8,7,6,5 and 4) based on the divisor alone and ignoring sign factors such as element or mode ?
In the end I felt that unless a significant amount of modern Numerology was introduced, relating to the meaning of numbers, the harmonics were not rigorous enough based on divisor alone.