I would assume the airbox is designed with wave tuning in mind. Just like the trumpets length and diameter the airbox will have an effect at what engine speed the air resonates perfectly.

By having an airbox which is not tuned to the trumpets then the system will not be as efficient and will have frictional losses an will not resonate properly I woud think.

I never studied carbon air boxes but my project in college was variable length intake manifolds and they basically worked on the above principal but oddly enough only worked at full throttle.

Here's a previous study. As it's an extension to the throttle body's the airbox would work in a similar way.

http://www.emeraldm3d.com/articles/cat/projects/post/emr-adj-length-intake/

There is also the fact that it provides less of a restriction to the intake of air.