We show that only 10 (17) CP-odd operators of the SMEFT give the leading, i.e. least suppressed by the small fermion masses of the SM, CP-violating contributions once we assume that all fermions are massless but the top (and bottom) quark(s). Since CP-odd operators typically lead to phase space suppressed interferences, we quantify the efficiency to revive the interference for various observables found in the literature but also for new observables in diboson production. Our new observables are found to be more efficient on the whole experimental fiducial phase space and we show the corresponding constraints on the Wilson coefficients depending on the luminosity.