Hi Philipp:
I am not qualified to answer your question as I am not very good at International style Latin. Since no one answer this thread yet, I will speculate. As lately when I do Cha Cha, Samba, Swing or Mambo, I keep reminding myself to maintain a smoother look that is to have my knees more flexible. That way, I had noticed thru the mirror that my shoulders or upper body no longer jumpylike.
I had watched some beginning beginners doing their Rhythm/Latin dances particularly Chacha, Mambo and Samba, their shoulders do bouncing up and down quite a bit. I am sure you have observed this too. If you look at their knees or legs, there are the problem due to the stiffness of knees as they are trying hard to get the steps right. As in Rhythm dances, one may say, obviously they had not mastered the proper techniques of "Cuban Motion". My current way of dealing with the overly bounciness is to think as I were to dance a smooth dance ( ie. Foxtrot or Waltz ). Does that make any sense?
Regards,
Keh Gough