Parameter study with base parameters defined in Table 3 for model PB_SBH. Upper left main-panel: Synthetic line profiles at phase φ = 0 (top left sub-panel), radial-velocity curve (top right sub-panel), equivalent width with corresponding reduced χ²-value (middle left sub-panels), semi-amplitude of the radial velocity curve with corresponding reduced χ²-value (middle right sub-panels), and total reduced χ²-value (bottom panel), all as a function of the disc’s base density, . The black dotted line indicates our best-fit by eye (see Sect. 4.1), and the blue dashed lines display the observed values with corresponding error-bars (blue-shaded area). Similarly, the top right to bottom right main-panels indicate the dependence of our measurable quantities on the disc’s temperature, , the slope of the density stratification, , and the micro-turbulent velocity, .