Left panels: The S SED (row a), and the corresponding fractional polarization (row b) as a function of the frequency, for a power-law cutoff EED, γ_cut = 5 × 10⁴, and p = [1.5, 2.0, 2.5]. The solid lines in the row b panel mark the Π_ν^ord evaluated using Eq. (1), the circles mark the δ approximation from Eq. (9) using $p_{\nu }^{(\delta )}$ from Eq. (7), and the crosses using $p_{\nu }^{(\delta )}$ from Eq. (8). The dashed lines mark the asymptotic power-law trend from Eq. (3). The relative error for the δ-approximation methods, w.r.t. the exact method (row c). In the row d panel, we report the best-fit of Π_ν^ord by means of a broken power-law function.