Oh, and I doubt the MP or EP would measure that differently but who knows with this strange beast. Still, they use the same basic driver and passive radiator design which seems to be accounting for these measurements.
I'm suspicious that the passive radiators are part of why these look so bad. They are essentially 6 driver diaphragms that react with the backwave produced by the driver, so maybe they have a delayed response from the driver that doesn't sound that bad, but is picked up in this type of graph. An interesting test here would be to measure a K141 of the same vintage, which uses the same driver, but without the passive radiators and with circumaural pads instead. And yet despite these pretty drastic physical changes, sounds almost identical to the Sextett, just slightly smaller soundstage. Too bad I don't have mine anymore.