I tried that (I have an HFT 2.0 at 18" from the floor, a pair of HFTs at 5’ mid-way between speakers, a HFT-X at 5’ between speakers and an HFT at 7’ high between speakers). When I added the Blackbox and Atmosphere XL4 is when I apparently lost height but gained so much more in width and tonal warmth. When I added HFTs on at 7’ above the 5’ HFTs, the balance was thrown off, too much highs relative to mids and bass. I also have mid-wall to the seating area 5’ high HFT 2.0 and 7’ high HFTs, and at the corners behind the speakers (they are literally corners with record shelving at an angle facing the room) I have 5’ high HFT 2.0s, 6’ and 7’ high HFTs.
Also, an anomally from the suggested SR setup is that I cannot put any HFT types on the face of the speakers (top, sides and rear work great). They tend to alter the frequency balance, especially bad is placing either an HFT or HFT-X below the dome tweeter or below the ribbon supertweeter. I also tried at 8 and 4 o’clock positioning. I just leave them off and voices, violins and guitars retain a beautiful balance of body and head. It’s only in Jazz Party opening cut and Abraxis that I lack the placement of the highs above my head which annoys my friend who has it all. He has ZERO room treatment, a congested room with speakers nearly flush against the wall and a 80s 27" tube TV smack in the middle between the speakers. Those little speakers (his own folded bass design) are remarkable, with fabulous soundstage (height and width) and all the other requirements put forth as well as high volume level without distortion. What they lack is body type dynamic punch (his room mitigates against that as well) like my system or a good horn system.