TTVs for a simulation of a planet with TSNR = 30 (contour map) as a function of the longitude λ_o and the impact parameter b. As shown in Fig. 3, O−C has positive values for spot-crossing events before λ_o = 0 and negative values otherwise. While there is almost no difference in the maximum values, their positions shift to longitudes closer to the center of the star for higher impact parameters.