Hi Ben,
This is an important question
Second to the concept of absorb/project is the Kua. With a/p we get an idea of yin on the front of the body absorbing down to the ground and yang on the back of the body projecting up. Doing this movement both the kua close when you absorb and both open when you project, but they are in their mid state or neutral state.
If I then turn to the right then my right kwa is closing and my left is opening, or you could say that the right is getting more yin as the left is getting more yang.
So you're getting a feeling to the balance and movement of yin and yang on the front and back with the balance and movement of yin and yang on left and right. Combined together it produces spiral energy.
At least this is my understanding so far
Steve