Fractional linear polarization, Q/I, as a function of magnetic field strength for different optical thicknesses specified at the top-left of each panel. The blue (red) curves correspond to the blue (red) component of the 10 830 multiplet. The dotted curve shows the result with the non-RT model, the dashed curve shows the result with the RT-flat model, and the solid curve shows the result with the RT model. Note: the vertical-axis scale is different in each panel.