Detection-weighted distribution of the effective spin parameter of BH-BH mergers for model M40.B with fallback decreased natal kicks (low natal BH kicks for low-mass BHs and no natal kicks for high-mass BHs) and for model M43.B with high natal kicks (all BHs, independent of mass, are subject to natal kicks drawn from a 1D Maxwellian distribution with σ = 265 km s⁻¹). We note that the average effective spin decreases from model M40.B (χ_eff = 0.05) to model M43.B (χ_eff = 0.004) as an effect of the natal kicks that tend to misalign BH spins and lower the effective spin (see Eq. (1)). For comparison, we show the 90% credible limits (blue arrows) and the most likely values (blue stars) of the effective spin parameter for ten LIGO/Virgo BH-BH mergers.