Well it seems that mr. Linkwitz changed his mind about that again

Here is a snip from his site about the new Orion+ with a rear tweeter for some dipole action in that freq. region:
"Yet, when I listen to ORION with added rear tweeters, calling it ORION+, I can only say that I have never heard sound reproduced as realistically in its dimensions of space, frequency and time. Sure, it is only an illusion and it all happens between the ears, but the ease with which I fall for the illusion becomes obvious when I switch back to PLUTO+. There the imaging is pin point analytical left to right in an acoustic space that has less depth and height than ORION and which by comparison to ORION+ clearly takes some effort to construct in my mind from the cues given. Sort of a re-programming after having heard ORION+."