Modal Jam Theory
When the plain symmetry of the tritone interval is intentionally avoided... the spiral symmetry of the golden ratio (and its reciprocal) is revealed as the catalyst for modulation.
While the concepts of 'Symmetric Modal Fusion' involve the entire circle. The study of 'Modal Jam Theory' focuses on 'half' the circle (the other half being seen/heard as a 'reflection'). These articles (The Power Of Limits) are an attempt to reveal why:
This first example shows where we draw this dividing line -- as we can see... our half (of study) is taken out of the middle by including the Dominant ('G') and its Tri-tone Substitute ('Db'):