Left: original counter-image 4b where a blue dashed line has been used to approximate its shape, the position where this arc intersects the BCG is surrounded by a red circle (a), and the angle (α) between arc 4b and the x-axis is shown. Right: counter-image 4b predicted with case 2b where position (a) is fixed to the same y-coordinate selected in the left panel and x-coordinate is chosen to correspond with a maximum of the rebuilt image. This counter-image is fitted to a straight line, which has a certain angle (α) with respect to the x-axis. This process is repeated for every model considered.