You've made this argument before and I still don't buy it. DI of a system in a room is not defined as DI is only applicable to free space. So using DI the way that you are is not reasonable. If we are talking about how speakers perform in real rooms thats fine, but then lets drop any DI discussions. If we are talking about DI then we have to assume that we are talking about a free field.

You room boundary extension concepts are grossly over-simplified and I continue to doubt that things work the way you hope they do.

Your dual axi-symmetric approach does work fine - agreed - if you can live with a cabinet that is now twice as wide. I made this point earlier too. You keep repeating your points as if you don't even read my rebuttal.