Predicted retained dust-to-stellar mass ratio for star clusters as a function of stellar mass and star cluster core radius, shown for cloud-scale star formation efficiencies ε_★ = 0.10 (upper panel) and 0.50 (lower panel). The colors encode log ξ_d = log​[ξ_d, 0 (1 − f_mech)] with ξ_d, 0 = 2.14 × 10⁻³. The dashed black curves mark f_mech = 0.5, and the solid black contours display log ξ_d = −4, the characteristic level inferred for blue monsters.