Using in defense
Whilst we practice this guard with the knee straight foward, you will need to angle the knee out to receive the attack head on. So if raising the right knee and blocking the opponents left kick, you will need to angle it more out to the right, to intercept the kick directly. If blocking a kick from the other side, then you will have to angle the kick and turn to the left (across the body) again, to block the attack directly.
Don't just turn the knee, rotate your body and guard also, so that you get your whole weight behind ur knee.
Learn to stand in the Yok Khao guard and turn the knee to intercept attacks from different angles and heights.