Extended MRI analysis for the analytical model given by a vertical magnetic field with radial power-law decay in Eq. (25). Left: Generalized instability criterion. Middle: Comparison between the generalized and standard MRI for the wavelength of the fastest-growing mode. Right: Timescale of the instability. We have considered the values with n = 2,  4 and C = 0.01,  0.025,  0.1 in the model defined by Eq. (25). The wavelength and timescale are shown only when the instability is active according to the generalized criterion, a transition that is marked with black dots.