Best linear fits of the correlation between median Einstein radii θ_E,med and lensing cross sections σ_7.5 for numerical and analytic clusters. The blue solid line indicates the best linear fit for numerical clusters (cf. Eq. (28)). The red dashed and the green dotted line indicate the best linear fits for cosmological populations of triaxial dark matter haloes (cf. Table 1) with inner profile slopes α = 1.0 and α = 1.5, respectively, assuming a WMAP1 cosmology. The lensing cross sections of triaxial dark matter haloes are systematically larger in the range θ_E,med ≳ 8″.