Slice properties of a fully varying profile in the monotonic azimuthal variations experiment, with either twists (left y-axis) or ellipticity gradient (right y-axis). The dashed vertical lines show from left to right the line at which the semi-major axis = 0.9 θ_E and the line at which the semi-minor axis = 1.1 θ_E, considering an Einstein radius of 2″. They separate the different regions considered for variations (see Sect. 2.2.2). The slices belonging to the different regions are represented with different colors and symbols.