Left panel: dependence of the amplification factor, defined in Eq. (34), on the amplitude of the initial MRI velocity field, V₀. Right panel: dependence of the amplification factor on the initial PI velocity field, v₀. We use the runs from Table C.2 (solid lines with squares). Each color represents a different initial PI amplitude, v₀, where the darker colors stand for larger values of v₀. The solid lines represent the fit from Eq. (45). The dashed lines stand for the amplification factor computed with Eq. (42), i.e., assuming no background shear. The black triangles correspond to the results from the numerical simulations of Rembiasz et al. (2016b), and the black solid line is the linear fit from Eq. (47).