Constraints on the q − a plane from the SKA sensitivity curve and assuming a primary black hole mass M₁ = 10⁹ M_⊙ at z ∼ 6.8. The dashed line shows the innermost stable circular orbit (ISCO), while the shaded region indicates the regime of detectability of the binary SMBH with SKA PTA The top axes show the observed gravitational wave decay time and the orbital period of the binary and the velocity of the lower-mass black hole. The range of velocities in the regime of detectability is of the order of 0.06c − 0.2c, ensuring good prospects for prompt electromagnetic follow-ups via Doppler boosting of the light curves.