I had B&W speakers in the CDM series which preceded the 703. The metal-domed tweeter was similar to that in the 703. The harsh and prominent highs did diminish with time over 3 years but never disappeared. The best single remedy that worked was to cut some thick felt pads and to fit them around and under the tweeter assembly using double0sided sticky tape. The felt must cover the angular edge below the tweeter to minimise diffraction effects.
But in the end I sold them to someone who thought that what emerged from them was exciting hi-fi sound.
But in the end I sold them to someone who thought that what emerged from them was exciting hi-fi sound.