Oh, very nice! Never thought of that configuration. I assume this may be one of the appeals of a daline enclosure?
Yesterday I received an email reply from Martin J. King about my cross section question, and this was his reply:
"The basket, cone and magnet will change the cross-sectional area of a TL locally. I have taken this into account a few times. But my experience has been that the changes in the SPL response have not really been that significant. At low frequencies where the wavelength of sound is so long, small local interruptions in the cross-sectional area are just not very significant."