Percentage of time spent during core He-burning as cool RSGs for all 20–60 M_⊙ models with α_semi = 100 and α_ov = 0.1 (non-rotating). The dashed lines represent the observed maximum luminosity of RSGs for each galaxy/our theoretical predictions for the HD limit in each galaxy such that models that lie above these limits must spend less than ∼5% of core He-burning at these cool temperatures.