Well, as Anabel had said, often people will change the flexion at the quarterline before and after X.
Say you are going left, you leave the track at M and make go straight while still maintaing the left flexion. At the quarterline, move it over to the right flexion. As you near X, increase the bend go through X and continue with a lesser flexion. At the quarterline, heading towards F, change the flexion and continue on.
Edit: I didn't see Anabel's post :)
"You know, for as long as I can remember, I've had memories." ~Colin Mochrie