Left panel: accumulated values of the RM along all LOSs that lie within the Galactic disk plane. All LOSs start outside the MHD grid with RM = 0 rad m⁻² and incrementally converge with each step size dℓ inward at the very observer position P1 where the RM reaches its maximum. The magnitude of the resulting RM signal at position P1 is shown in Fig. 5, left panel. Gray contours indicate the electron density and the vector field represents the magnetic field strength and orientation (see Fig. 2). Red lines are the tangents B–H detected by the RM signal, whereas blue dots represent the tangent points derived from the column density map shown in Fig. 6. Right panel: same as the left panel, but the relative change is plotted along all LOSs as they approach P1.