Hitting down is a function of the swing arc bottoming out just after impact with the ball. Ball position is then critical for you to make contact in the fassion you're looking for. Also take note of how strong your grip is, and what kind of motion you make through impact. Generally your motion through impact falls into one of three categories.
1) Pull - like pulling on a rope in a tug of war contest
2) Roll - The arms rotate
3) Throw - The hands and wrists are used
Each of them brings the club through impact in a slightly different manner. A pull through impact will have the clube move through impact on a much more straight line... a roll has a very consistent arc of the clubhead... a throw is a very steep approach into impact. Bellow is an illustration.
For someone with a throw motion, a downward sense will be more apeasing since the club will shallow out much more abruptly. This downward sense is directed AT the ball. For someone who releases with a roll, a sense of moving the club forward or out toward the target will delay the bottom of the arc to just in front of the ball. And finally a pull is used in iron play as a very downward intention with the hands required to be well ahead of the ball. The downward sense is actually somewhat aimed ahead of the ball since the hands need to be much more ahead of the ball at impact. The feeling of "Driving it to China" is almost required due to how long the club must travel more linearally (straighter-not as circular).