It was not as much as space issue as they could have used also a large tapered tube like for example B&W but with the meta absorber they also reach very high absorption rates which are higher than with typical damping material:
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The Meta generation tweeter has generally lower distortion compared to the previous generation
How much each individual of these improvements contribute to what is something you can only ask the KEF engineers who participate here.
Audibility of those is even a harder topic which in the