Comparisons between R_Fe predicted by photoionisation models with different input parameters and R_Fe measured in our sample. In each panel, the green line indicates the mean R_Fe found in the SDSS sample that matches the JWST sample in terms of Hβluminosities and FWHM; the magenta shaded region corresponds to the value found in the JWST sample; the red shaded region corresponds to the value found in the JWST sample excluding sources with X-ray detections, which also happen to be the strongest Fe II emitters among the faint AGNs. The grey shaded region indicates the plausible range of metallicities in the NLRs of the JWST sources based on the T_e method for a subset of the JWST sample. Photoionsation model predictions are plotted as a function of the metallicity, Z/Z_⊙, and are colour-coded by the ionisation parameter. Left: solid lines and dashed lines correspond to models with and without a hard X-ray component representing the hot corona contribution to the SED, respectively, Right: solid lines and dashed lines correspond to models having N_H = 10²⁴ cm⁻² and N_H = 10²⁵ cm⁻², respectively.