X should be your widest point of the loop ie loop out from M towards X then back to F, not sure that makes sense really but I know what I mean! I'll see if I can find you a diagram.
Sorry can't find one - but do you have dressage diagram membership cos you can see the diagrams of the tests on there if that helps?
As Jo said X is the widest part of the loop, so in a way u ride MX, then XF but making it a loop shape.
I have ridden that test about 5 times since end of June, so feel free to ask any more questions.
Tip: make sure you sure a clear difference in medium canter to working canter as a lot of horses I have seen, don't show a big enough difference.
That is what I am worried about as it is quite a small area to show it in... I am considering putting my small spurs on as she really lifts through the back with them in the medium and it is more obvious but she is not really schooled much in them yet, I am just starting.
Yes - I have judged it several times - remember to ride the loop AND the 15 metres circles accurately - so many marks are needlessly lost through carelessness.