ok, like i said, back of the envelope.
i just took a guess at the inputs for hornresp using the diagram in post 1.
i kept getting a big peak in the 150hz ballpark and thought i was just missing something.
poked around on the interwebs for a bit and found a measured scala in the center of a large room. that is the aqua line in the plot mess.
the black line 2 was my guesstimation. i wouldn't call it accurate, but it does predict a large peak and a fairly early rolloff.
the plots are on different scales, so i adjusted them so the frequencies all lined up as well as the vertical spacing for a db. then i just shifted the graphs so the level of the peak was the same, as this gives the best comparison.
as for black line 1, i tried to put a port on the larger cab and tune the thing to around 40hz. however, doing so kept giving me a peak at 50hz. i've not modeled a ported enclosure front loaded horn before, so i dont' know how close it is to actual results. with a standard ported cab, the peak should be right around the tuning frequency.
it is all quite a mess, which is why i didn't post it. but since you asked...