R versus wavelength for M4327. The logarithm of the ratio between observed and theoretical (Case B) line ratios of hydrogen lines to Hα, R, is plotted as a function of wavelength. Colored lines represent the R vs λ relationship predicted for different values of E(B − V), given the Cardelli et al. (1989) (solid lines, R_V = 3.1) and Gordon et al. (2003) Small Magellanic Cloud (dashed lines, R_V = 2.74) attenuation curves, respectively. The black curve reports the relationship obtained by performing a least-square fit to all available hydrogen lines ratios (for a Cardelli et al. 1989 law), whereas the purple curve represents the best-fit E(B − V)_cov and f_cov values obtained by adopting the dust-covering fraction model by Reddy et al. (2025).