Log-log fit to the simulated initial cluster mass versus the present-day stream mass using weighted OLS regression in two mass bins (boundary at M_stream = 1700 M_⊙). Here we include only systems with L > 1000 kpc km s⁻¹. The fit has a slope α = 0.96. The blue band shows the 95% prediction interval based on empirical scatter, and the crosses show the possible predicted initial cluster mass based on the fit and the 95% interval. The gray dashed line represents a reference case where M_initial = 10M_stream.