I noticed that the DI didn't support what I was saying, but chose to ignore it.
[O.K., I get that now.... ]
Naw, it's de riguer - PT Waveguides at ZilchLab.
For a symmetrical waveguide, the little work I did with the Engebretson indicated it "promising." Maybe I'll continue some with that:
http://www.ddshorns.com/catalog.php?page=ENG190Pro
If it's good, someone should document the profile for DIY.
["Family".... ]