Yeah, have this problem, too at times. I'm also using a new XL (bought it in January) and swipes are sometimes not registered right. Though you'll get the knack of how to swipe.
Though EMS are even worse. In BMS and FMS, a good is received fairly easy. So, a little bit off isn't bad. EMS, however, seem to have a different timing. I heard, those stages run by 30 frames, though input is still at 60 frames. Now, being not good in technical issues, I'm not sure what this exactly mean, but as said: I believe this makes the timing of EMS different.
This used to make me so mad. For me, the reason was that I was doing most of the slide in the air, and only gently brushing my screen - hence it counted as a Touch. Flip, I remember Saber's Edge: so you know the opening is really fast, tap-up-down-tap-down-up-tap-tap, six times I think? And after that, it goes tap-tap-downleft, tap-tap-tap-tap-upright? FOR THE LIFE OF ME I could not get that upright to register. I really had to try hard to push my stylus down onto the screen, and even then I still sometimes only ended up touching it.
So yeah, it's a common problem; but I haven't had an unexpected Bad slide in months, so I guess it's a problem you naturally work out how to solve if you play enough.
EMS's require far more precision than other Scores and are the earthly manifestation of hell. >:[