Thanks, Ian.
I did the impedance sweep and added it to the post above.
Also did an audio sweep to be sure there was no buzz/rub from installer error.
I don't have a 16-Ohm version of the crossovers I'm using here, so it's not that.
It looks like the 2426H driver characteristics are sufficiently altered with installation of D8R275ND as to require different compensation, is all.
In a former life, I'd be dismayed.
CLIO will tell us what to do....