Schematic shows the locations of the radio sources for the +Z and -Z solutions of Equation 4. The Sun is located in the middle as an orange circle, with a horizontal dashed black line representing the POS. The vertical dashed green line represents the Sun-Earth LOS. The dashed blue and red circles represent the plasma spheres of density equivalent to the observation frequencies of the innermost and outermost radio sources at R₁ and R₂, respectively, under the Newkirk model assumption of spherically-symmetric density distribution. The impact parameters r₁ and r₂ are the projection of R₁ and R₂ on the POS. The dot-dashed blue and red circles are the circles passing through the impact parameters r₁ and r₂, respectively.