For a right hander, if you step your left leg in under the table you would have more angle to go somewhere other than cross court with your forehand but you'd be playing something a bit longer or nearer the table height.

But if it really is a short ball,  as Zwill said, it has to be your playing hand side leg.  That is because you have to reach over sideways.  I'm pretty short so my arms will be shorter too, I have to step in with my right leg so that my right playing arm can reach near the net.  

Since I stand in the general start position, if the ball lands on my left I have to play backhand and if it lands to my right I have to play a forehand.

However it seems that for half long or truly short balls, you kinda have to step in with your right foot otherwise you won't be able to reach the ball even...

Unfortunately, against pips sometimes this is kinda mixed up....

With BH it's almost always the right foot unless the ball exits the sides of the table where you'll have to step in with the left foot, much easier to use.

If its trully short it is always the playing hand side.

Anywhere else on the court you should be getting into your optimal shot position, as you know, right foot back for forehand.  That does not mean step forward with your left or step back with your right.  It all depends how close to the optimal you can get.  

Even the pros end up doing the optimal feet the opposite way when surprised and still manage to get away with it with less than optimal body work and stroke etc.

Just came across a new favorite video because it's all slow motion, so much stuff happens that is hard to see the quickness of TT. 

https://www.youtube.com/watch?v=ckeHBFFBlxw" rel="nofollow - https://www.youtube.com/watch?v=ckeHBFFBlxw