Effective aligned spin parameter, χ_eff, versus primary mass, M₁ (top panels), and secondary mass, M₂ (bottom panels), of all BBH mergers from the computed model clusters of Table A.1. For each model merger, χ_eff values for a number of random orientations of the merging BHs’ spins are obtained (Sect. 3), which are shown as a data point (mean value) with a vertical error bar (range). The legends of the data points are the same as in Fig. 1. The error bars (in a dashed line and solid line for mergers from the W₀ = 7 and W₀ = 9 models, respectively) share the same colour code as the corresponding data points. The LVK events GW190521 and GW190403 are highlighted with two empty squares, which are coloured differently for improved legibility and they do not correspond to the colour code.