The R.A.–decl. distribution of the sample clusters. The green plus symbols denote all the galaxies selected from the DESI and SGA catalogs with ∣z_spec − z_cluster∣ · c < 3000 km s⁻¹ and projected spatial separation ≤5R₂₀₀. The blue circles indicate cluster member galaxies selected using the phase-space diagram shown in Figure 1. The dashed orange circle at the center of each panel indicates 1 × R₂₀₀. The red circles highlight the locations of massive galaxies (﹩\mathrm{log}({M}_{* }/{M}_{\odot })\gt 11﹩).