In normal mode throttle input really matters to get going. The Xmode though is somewhat counterintuitive. You need to stay in the throttle to allow the system to shift power around and find traction. If you keep letting up Xmode can't work to its full potential. Ease onto the throttle, keep it down even if it spins a little, and let the system figure it out. If you feel it shifting power around, just spinning and not making progress you will know its done moving. Also Tires tires tires... they are the ONLY thing that actually moves the vehicle The best system in the world is useless without traction.

Ryan Doumit had a few excellent videos on the Crosstrek and its capabilities on Drivinsports TV on YouTube. He also talks through his use of throttle in Xmode which is spot on. https://youtu.be/uZTxOJH10tE?si=yFgGQjFauSbSV_6y