Please tell me if “XS size” is the size of an old mobile phone or the size of an iPhone.
The breakpoints are not devices as such. But ranges of width for the viewport (browser window). They are allow for a container to be divided by 12, and allow for multiple different screen sizes / devices.
Eg.
XS is anything less than 576px wide
SM is 576px to 767px
MD is 768px to 991px
LG is 992px to 1199px
There are also XL and XXL as part of the bootstrap scheme. But Blocs treats LG as the largest.
Bootstrap is also mobile first. That means if you set a style at the XS breakpoint, it will apply to everything unless you add another style on a wider breakpoint. Although sometimes Blocs seems to be inconsistent in following this rule 
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I don’t understand anymore, but I’ll further examine and think about what you wrote, thank you very much.
Sounds like Blocs should implement the two larger breakpoints. More work for Norm in the future. 
I guess you’re right… all of us.