Your article would be IMO much more fun and interesting, if your author Troels had set up the 802 s3 as designed from the factory optimized with the BAF. Then one could see what his mods accomplish versus a properly set up 802M s3.
https://www.kenrockwell.com/audio/b-w/800-series-bass-alignment-filter.htm
taken from ^^
Bowers and Wilkins' Matrix 800 series of speakers from the late 1980s through the mid-1990s were designed directly to John Bower's vision as part of a system incorporating an active, dedicated low-level filter in the preamplifier signal path to optimize the bass performance, not only in frequency, but also in the time and phase domains.
This dedicated bass equalizer, also called a variable high-pass alignment filter, was often included with the speakers since its frequency response is an integral part of the systems' sixth-order design.
Without this equalizer, the naked B&W Matrix speakers are a vented fourth-order design, specifically in a Bessel alignment. "Fourth-order" is an engineering term that refers to all vented and passive-radiator speakers; sealed boxes are "second order."
Troels comments at the start of the article.
Before starting any measurements I set up the speakers in my living room and replacing my ATS4, I experienced a somewhat smaller speaker with less visceral impact in the bass area and a somewhat less weighty lower midrange presentation, giving less fullness to vocals.
The sonic symptoms he describes can be attributed to running without the bass alignment filter. I say this based on personal experience having owned at one time all of the matrix line. Sill own matrix 800's.
Now the thing that is even more curious to me. He does link the owners manual in his article. The owners manual clearly states the need to use the BAF to achieve the frequency response that is documented.
Cheers