the "across" is a function of body rotation and pronation. you are not trying to swing across (in fact you try to swing as much in line with the ball exit path as possible. but since the swing is rotational you will not be able to hold that line for more than a fraction and then it goes "across".
for a CC shot you really hit "across" but only compared to the side line not ball flight.
the across is just a combination of the upward brushing and rotation (of spine and arm) it's nothing you should do intentionally. FYB has a good video about that. they describe the WW forehand and the coach says the worst thing you can do is swing normally to the ball and then try to rip the rackethead across the back of the ball. the ww finish should be a natural consequence of the upward swing path and rotation it is an effect and not a goal.
Last edited by dominikk1985; 12-04-2012 at 02:25 PM.