Everyone has a strong direction for their lines, I have seen it discussed by many people. Personally mine is kinda down and leftish ... so I am always rotating canvas with things I am working on I don't think that there were any "rules" to these assignments
However, I personally was looking at this solely as practice and tried to turn my body differently so that I wouldn't be using a strong stroke, gotta try to use those muscles in different ways so that they get better right?
Lets see that cintiq one! very curious how you feel the difference, my non cintiq wacom has gone the way of the dinosaurs... well the dinosaur toys that my kids play with, because they use it as a little table for tea parties now. 