The diamond stays on the top as it got this little catier logo at the bottom which makes diamond always stays where it should be. The bracelet just flips naturally n beautifully with your hands move, making you non stop staring at it lolll. For me I like both of the size as them got different purposes. The xs one can add a little sparking into your stacks without too dramatic n tacky while the small size can be more sparkling n visible with elegance look. However since you've got a trinity cord bracelet, which can be a huge bracelet compared to the xs diamond bracelet, making the XS disappear in your stack, if I were you I would go for the small size so it an stack with the trinity cord bracelet with a better balance.
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The shorter n smaller Cartier logo is the XS size whereas the longer n bigger logo is the small size.