Spectral index values as a function of environmental density and stellar mass for passive galaxies in J0152.7 (red) and J1252.9 (blue). Differences in D_n4000 with stellar mass and density are similar in both clusters, apart from a slight but notable decrement in D_n4000 for J0152.7 passive galaxies in the low-density regions with respect to their counterparts in higher-density regions. There is also a marginal (due to low S/N) elevation of H6a among J1252.9 low-mass galaxies with respect to J1252.9 high-mass galaxies. A modestly significant H6a difference is found between the J0152.7 intermediate-density population and the J0152.7 high-density population.