Greetings to all:
For whatever reason, there seem to be many variations in the footwork represented by the younger relatives, disciples, and students of Yang Chengfu. There is even greater variation if one takes into consideration Yang Style that comes through earlier generations of the Yang Family.
From what I have come to understand, all footwork requires various compromises between mobility, stability, power, consistency, and flexibility. For instance, using an 80-degree angle for the back foot simplifies the transition into Single Whip, but would complicate the backward stepping that follows Fist Under Elbow and each of the Repulse Monkeys. Using the same footwork throughout the form simplifies learning and reinforces certain principles, but reduces the scope for optimization.
I think the hidden compromises are one reason that “oral transmission” is necessary to understand deeper principles of the form. There may be greater implications than are immediately apparent to changing the back foot between 45 degrees, 60 degrees, 80 degrees, and 90 degrees, or even keeping the feet parallel.