Swing path and angle of racket face when hitting DTL off a cross court shot
Some time ago, my son had the privilege of taking a few lessons from an excellent coach (he was a former pro himself and a former Olympic coach for a South American country). The coach said that you should aim at the back (directly behind) of the ball when hitting DTL off a cross court shot. I took that to mean the racket face has to be perpendicular to the sideline which means the swing path naturally is parallel to the sideline.
But, this does not make sense if you believe the rule that the angle of incidence=angle of reflection. In other words, the racket face and the swing path would vary depending on the angle of the cross court shot, the more angled the cross court shot, the more your racket has to face towards the center of the court if you are trying to hit a DTL shot.
What am I missing here? Was the coach wrong in telling my son to aim at the back of the ball or does the force of the swing change the rule of angle of incidence=angle of reflection?