Ratio of the non-linear power spectrum in f(R) gravity to ΛCDM from the fitting function in Eq. (27) for three different values of the |f_R0| parameter, namely, 5 × 10⁻⁵ (blue line), 5 × 10⁻⁶ (purple line), and 5 × 10⁻⁷ (orange line), as a function of scale, k, evaluated at two different redshifts, z = 0.25 (solid lines) and z = 1.75 (dashed lines). These redshifts correspond approximately to the means of the first and last lensing tomographic bins of our survey, respectively (see Section 4). The fitting formula designed in Winther et al. (2019) is not defined outside 10⁻⁷ < |f_R0| < 10⁻⁴.