Extrapolation of the magnetic field computed using Eq. (11) (blue lines), case A (red lines), and case B (purple lines) down to the event horizon radius r_H = 0.6 R_S (highlighted by the blue dashed line) assuming B(z) = B₀(z/z₀)^2ψ. See the text for details on the different dependence. The orange dashed lines indicate the upper limit on the magnetosphere radius, namely r_m = 2.1 R_S with η_d = 0.1 and r_m = 5.3 R_S with η_d = 0.4. The orange box highlights the range of variation of the expected saturation magnetic field strength in the MAD scenario, while the light green box indicates the poloidal field strengths inferred based on the magnetic flux.