Left panel: Joint marginal error contours 1 σ and 2 σ on the cosmological parameters for a flat f(R) model with |f_R0| = 5 × 10⁻⁶ (HS6) for the GC_sp probe. In black dot-dashed lines the quasi-linear case (k_max = 0.15 h Mpc⁻¹), in solid green the baseline pessimistic case (k_max = 0.25 h Mpc⁻¹) and in purple the optimistic case (k_max = 0.3 h Mpc⁻¹). Right panel: Same as in the left panel but now comparing the pessimistic baseline case (solid green) against the more realistic models, with increasing level of complexity. In yellow the addition of scale-dependent Q-bias, in dark blue the addition of free σ_p and σ_v nuisance parameters at each redshift bin and in cyan (dash-dotted line contour) the addition of both terms together for a total of 10 extra nuisance parameters. The loss in constraining power when using this more accurate model is similar to the loss in constraining power when doing a quasi-linear scale cut.