Maybe I'm reading that chart wrong, but the widest difference is about 6dB apart at 20Hz. By 30Hz, 3dB. As it goes up through the bass and mid bass, they are all huddled together tight with less than 2dB difference all the way up to 1kHz. Any difference in the sound of the bass would have to come from distortion or dynamics or something like that, not frequency response. Weird... Maybe I'm looking at a different chart than you are.
Coming from the speaker world, you should know better than this. A slight change in speaker alignement has a limited impact on the frequency response but the effect is quite visible in the impulse response / transient response.
I am not sure you have experience with the lcds and senns, but the bass presentation is rather different.
Misinterpretation. I am extrapolating what i heard (th900 vs. rp prototype) with what is shown (th900 vs. pm1).