Schematic overview of the parametric spin population model described in Equation (3). Below a mass cutoff ﹩{m}_{1}\,\lesssim \,\tilde{m}﹩ the population is described by a mixture between a component whose spin directions ﹩\cos {\theta }_{1(2)}={\hat{{\boldsymbol{\chi }}}}_{1(2)}\cdot \hat{{\boldsymbol{L}}}﹩ follow a truncated Gaussian distribution (mixing fraction ξ) and a component with isotropic spin directions (mixing fraction 1 − ξ). Above ﹩{m}_{1}\gtrsim \tilde{m}﹩ the spins also follow an isotropic distribution. Each of the three components are allowed to follow different spin magnitude distributions.