Comparison between the retrieved (y-axis) and input (x-axis) relative magnetic field strengths (δ〈B〉). The synthetic observations were normalized to the template using a rolling median with a window of 100km s⁻¹. The red squares and green plus symbols (‘+’) show the results obtained before and after re-normalizing the models used to computed F_k - F₀ (Eq. (4)) with a 100 km s⁻¹ median filter, respectively (see text). The black line marks the equality. This figure illustrates the need for careful re-normalization of the models to avoid biases in the results.