Actually, I've found they really don't. For example, the single circle that you make going right to left- I've made really big circles and really small ones and both worked. More important it seems is pressing the button before I start and letting go when I'm done, and not getting anything else in the mix while I'm doing it. I think there's a tendency to let go too quickly, right near the end of the pattern, in order to get it to register quickly.

The heart is the easiest if you just remember to go up as your first movement. I've watched friends mess it up, and mostly it's because they tend to try and make a circle rather than a heart, going out instead of up as their first movement, and this never works. However, I've almost never failed this one if I remember to go up first.