⟨PA_∞⟩ versus activity cycle for the two phase clusters: G₁ and G₂. G₁ refers to the ⟨PA_∞⟩ measurements made at around Phase 0.359 (MJD 59894, 60303 and 60352) and G₂ at around Phase 0.400 (MJD 59274, 59568, 59944, 59993). See Sect. 3.2. The black markers are used to denote those ⟨PA_∞⟩ measurements with only one burst. The top x-axis shows MJD of the ⟨PA_∞⟩ measurements. We emphasize that the reference MJD of the top x-axis is that of the periodicity model of FRB 20180916B.