Please re-read what I posted. This is due to room acoustics (Edit: I suspect you may know this already, but it’s being lost in translation, so please forgive if I’m missing something). I brought this up as the tilt seen in the Harman speaker target isn’t for more bass. It’s principally due to acoustics. The speakers are indeed flat on-axis when I take semi-anechoic measurements. If you were to try to make the steady-state room response flat the speakers would have too much treble.
Edit, again: I dug around a bit and found some measurements in the far-field for the S55 speakers by themselves with no EQ or sub reinforcement, and the steady-state in-room response tends to inversely track the directivity of the speaker.
View attachment 241714
View attachment 241715
For completeness, here is the gated on-axis response at about 1m. It is necessarily flat, but the S55 has some directivity error in the cross-over region as well as some beaming and eventual diffraction from the tweeter/waveguide above about 6-7 kHz.
View attachment 241716
I think the only speaker that would have a flat in-room and "on-axis" response would be something like an mbl with radialstrahlers as it will have a more or less constant sound power across the audio spectrum and a DI very near to unity. Stereophile has some measurements posted, and above the transition region the response is fairly flat due to, well, every axis being "on-axis":
MBL Radialstrahler 101E Mk.II
Hopefully this makes some sense (and is at least somewhat correct).