The revised response curve looks exactly like you had advised, quite flat with a smooth extended drop off. Also, at the SPL's I listen at the response is comfortably under xmax > 35Hz.
Understand I was in no way questioning the 2pi tower design or how it sounds, just trying to get a handle on sim's. When I saw what modeled xmax was doing I was a little shocked, which peaked my curiousity to understand it.
Thanks for the education. I'll feel a bit more comfortable now in using these programs, as I try to re-purpose some Peerless 12" SLS woofers into modal smoothing duty .