Hi Jovi, our products are for web-solutions so our breakpoints are focused on larger screen sizes. That being said, our Small breakpoint ranges from 768-1279px and captures tablet to small desktop screen sizes. This size is excluded from the fixed grid due to the smaller size.

The Medium breakpoint starts at 1280px and includes 24px of side-margins. So it's really 1232px for content. We wanted the fixed content to allow for the full 1280px for content to allow seamless transition from breakpoint to breakpoint jump. This required us accounting for the 24px of side-margins.

1280+(24*2)=1328px

Hope this helps! This solution works for our product teams, so it's dependent on your needs.