The probability distribution function P(>μ, z_s = 6.51) is shown for β = 2.8 and β = 3.6, and for magnification values between μ = 1 and 100. The dashed vertical line indicates the magnification factor for the lensed quasar reported by Fan et al. (2018), with the 1σ uncertainty level shown as a shaded region. Note that P(μ > 50) = P_obs for β ≈ 3.2.