Left panel: O abundance (relative to hydrogen nuclei). The black contours are iso-temperature curves at 200 and 1000 K. Central panel: optical depth of the line (blue) and of the continuum (black) in the top mini-panel, below is the cumulative flux of the line, which shows which percent of the final flux is built and where, the lower mini-panel shows the oxygen density, the contour indicates where the contribution to the line flux goes vertically from 15% to 85% at every radius. Right panel: FUV (top) and X-ray (bottom) heating rates. These rates are obtained integrating the volumetric heating rate Γ over the volume of the [OI] emitting region for every model. Averages and error bars have the same meaning as described in Sect. 3. The first two panels are taken from a representative model with L_X = 10³⁰ erg s^-1, L_FUV = 10³¹ erg s^-1, a_min = 0.1 μm, a_pow = 3.5, and ϵ = 1.5.