Well, all the measurements that led to setting the crossover up to 16.5kHz were based on this assumption: we want to cross the drivers over, not blend them. One driver should be the main contributor, or the other one, thus maximum frequency specificity.
It's a good idea, anyway. But in listening to Bass Erotica and We Want To Be Loved, it seemed to me the magic I heard the other night, the magic was gone, even replaced by a barely noticable harshness (making you think the answer would be to turn the high pass up even more, get them tweeters outa there).
So I went back to 14.2, and the magic was back. It was pretty good at 14.8, quite good at 14.5, and virtually unlistenable at 13.9. At 12kHz, it was intolerable. So 14.8-14.2 seems to be the sweet spot, with 14.2 having the most magic.
Doing a sweep, it does not appear that the Elac supertweeters are contributing much to the peaks of the Acoustat below 14kHz. At 13.9 kHz specifically, turning off the Elacs only reduced the level of a peak by 1dB.
But played by themselves, the Elacs would now be acceptable with another driver crossed over as low as 12khz, according to previous tests. So the current crossover seems to be more of a "blending", with the Elac and Acoustats complementing each other in the range 12-14kHz.
Strangely, however, if I could make the Elacs acoustically cross exactly where I want, I would choose 14.2, and that is also what I have dialed in, but based on listening tests rather than measurements.
An overall sweep shows barely any difference, perhaps the 14.2 provides somewhat greater stability and non-directionality thanks to greater coverage by the omndirectional tweeter rather than the narrowing beam of an electrostatic driver at its upper limits.