Can’t answer the hull shape difference between the X and SX.
I place the Nauticurl just above the lower shelf with the wedge just in line with the transom.
Here is a video of my niece surfing goofy side, first time ever without the rope.
https://youtu.be/Mhq6C6rDxWAThis was with the setup I mentioned above.
I stacked up 2 Nauticurls and it made the pocket a little better and seemed to give even more push.
Will try to get a video of natural side tomorrow.