Frequency ν_d and amplitude A_d of the maximum depression of the first dip in the PSD ratios, plotted as a function of the source height (top and bottom panel, respectively). Open and filled points in the bottom panel indicate the data for the α = 0 and α = 1 case, respectively. Black, red, and blue points indicate the data for θ = 20,40, and 60 deg, respectively. The horizontal dashed line indicates the value A_d = 0.7.