PNG bias parameter p as a function of M_halo for different analysis choices. The green symbols represent the fiducial choices, while the grey dashed line represents the universality relation (p = 1). In solid circles, we use the best fit to Eq. (15) for estimating the power spectrum variance; in rings, we use the extrapolation method. The shaded areas represent the 1σ, 2σ and the 3σ regions (from darker to lighter respectively) around the value of p we find in Eq. (19). Masses are shifted for visualisation purposes. Panel a: variation in p with changes k_max (see Sect. 7.1). Panel b: constraints on p by considering different methods to compute σ(P(k)), namely: standard σ_S(P(k)) (blue), direct fit to FASTPM mocks (orange), best-fit to Eq. (15) (green) and extrapolation of Eq. (15) to the mass bins (red) (see Sect. 7.2).