Not in the same way as the AKG K371s. EQ makes the 6xxs sound more open [to these ears], but the character of the sound is different. When listening to the K371s, John Martyn's "Solid Air" come to mind, there is a sense of real texture to plate echo and such with the closed-back AKG 'phones, more of a sense of openness with the Sennheiser 'phones.
And here I'm blatantly unable to cite any real scientific papers, so let's speculate. If I'm correct, it's recommended that recording and playback spaces have flat RT30/RT60 (reverb dropoff by -30 and -60 iirc).
Then, K371s, due to proper midrange & bass smoothness and lack of roll-off let the plate echo happen, low THD in bass & mids don't obscure the -30 thru -60 tails in that range. Yet, they somehow lack the proper treble (I'd say, 6-20k) HRTF fit and some smoothness.
The 6-20k are well-done on HD6xx range and thus the open sound is happening due to proper reverb structure & evenness (keep in mind that we're talking -30 to -60dB) of response. Does thay make sense? I'm just looking for the source; right now I feel that % THD is really useless, since we're always dealing with miniscule details and one-two dB difference might cause the reverb to be unnatural easily. That shows how flawed the whole measurement process is due to lack of ability to make real treble measurements. Happily, we can assess smoothness of lower ranges.
Simply, overall smoothness & THD highlight different parts of reverberance, thus ending up in different soundstaging.
The overall consistency of reverb & lack of spatial cues - mostly reverb - masking could paint the full soundstaging image in the FR domain, abstracted away from other factors. Layering must be gone when the reverberation in any range overthrows the harmonics of instruments that engineer wanted to show up close.