χ² obtained by combining the IFP lead angle by the IPT radio occultations. Panels a and b are obtained from the reference IPT case by multiplying W₃ in Eq. 1 by 0.75 and 1.25, respectively. Panel c is obtained by converting the protons into O⁺ to verify the effect of the high-latitude plasma. Panel d is obtained by reducing the time window used to calibrate the background and increasing the window used to compute the residuals (see text for details). Red dots indicate the absolute minimum and magenta lines mark the 1σ, 2σ, and 3σ confidence levels.