It looks like the two pics you posted are of different systems, the first being slot loaded PP, and the second (full-system) showing a "traditional" IB. You also seem to be confirming my intuitive hunch of potential sound benefits and horn matching using mild compression loading, or exhaust area < Sd. I want to explore further.
Can you share further about your design inputs / criteria?
For instance, the drivers I'll use are 4 x Aura 1808, Qts = 0.19, Fs = 24 Hz, 2 each in separate L + R manifolds. These numbers differ from traditional IB drivers, but I'm not discouraged from auditioning them in an IB configuration.
Also, what guidance, if any, wrt: exhaust area? Your comment about observing rising Q and lower Fs using compression are encouraging.