Log-log fit to the simulated initial cluster mass and the present-day cluster mass using weighted OLS regression in two mass bins (boundary at M_cluster = 8000 M_⊙). Similar to Figure 5, only systems with L > 1000 kpc km s⁻¹ are included for the fits. The lower-mass fit has a slope α₁ = 0.53, and the higher-mass fit has a slope α₂ = 0.66. The blue band shows the 95% prediction interval, and the crosses show the possible predicted initial cluster mass based on the fit and the 95% interval.