Proportional drop in intensity contrast between disc centre and μ = 0.2, 1 − C( μ = 0.2)/C( μ = 1.0) at the Fe I 6173 Å line core (red) and 1700 Å (blue). The plot points denote the estimate from the intensity contrast CLV profiles in Fig. 2b. The curves follow the solution from the empirical intensity contrast models (Eq. (2) and Table 1). The dashed line marks the minimum of the Fe I 6173 Å line core curve.