Grid results: predictions of selected line intensities and model parameters, for Z_bin = 0.5 (top panels) and Z_bin = 0.1 (bottom panels). Color scheme: increasing initial density from 10^0.5 cm⁻³ (light green) to 10^3.5 cm⁻³ (dark purple). Symbol size: large symbols correspond to small inner radius (large U) and small symbols to large inner radius (small U). Dotted lines connect models with the same inner radius, solid lines connect models with the same density. All observations are overplotted in orange and galaxies in the metallicity bin plotted are highlighted in red. We note that the error bars are large because they include abundance uncertainties (assumed to be 50% of the flux). The PDR covering factor is set to unity. Top right panel: quantitative indication on how the C/O abundance ratio affects the grid predictions from Z_bin = 0.5 to Z_bin = 0.1. Other effects due to metallicity (e.g., stellar spectra, column density, etc.) are discussed in the text.