So there is this picture that is circulating on the internet that is showing the FC31 compared with the new Korean KF21. The tourcraft looks similar at least from the side and this is completely normal because the aircraft with geometric style tend to look all the same. However there is a detail that actually betrays the different design points of the tourcraft. It's the air intakes in the case of the FC31 RDSI intakes, so intakes that give their best at high subsonic low supersonic speed. In the case of KF21 those are classic wedge intakes. They are tilted on the side and probably there is a mobile ramp inside but those are intakes for higher supersonic speeds. The KF22 design has been optimized for a speed that allows to give the weapons to lot energy when they are released that the tourcraft have been designed with different rolls in mind.