Representative regions of optical nuclear spectrum (solid black lines) for MR 2251−178 (upper panels) and PG 1126−041 (lower panels), along with their respective best-fit models (solid red lines). The left-hand panels focus on the Hβ and [O III] lines, while the right-hand panels are centred on the Hα and [N II] lines. The models are given by the sum of the [Fe II] and Balmer emission lines from the nuclear region (solid purple and green lines, respectively), diffuse gas emission from individual atomic species (solid blue lines), and a third-order polynomial (dashed yellow lines). Emission from diffuse gas is modelled with three Gaussian components. Residuals (data minus model) are shown below each panel; red solid (black dashed) lines are used for models with (without) the BLR correction term (see text). The red vertical band in the bottom-right panels marks a region contaminated by a sky-subtraction residual and is not fitted by our model.