Symmetry. The Dorian scale is symmetrical around its tonic note. One might say that the sense of G-centricity in Block 5 and C-centricity in Block 6 derives in part from contextual factors (like harmonic support and rhythmic emphasis) and in part from their central position in the underlying symmetrical arrangement of the tones. Over the course of the music from the beginning, the center of gravity has slowly shifted downward.