All else is never equal. Bass inhabits its own world. I haven't seen a 2.7 FR graph, but the 3.7 goes perhaps 5hz (more or less) lower than the 2.4, perhaps 1/6 octave - that's not much. But the tuning of the smaller model 2 enclosure to reach that deep induces more reactivity and therefore more difficulty for amplifiers. The 3.7 bass is an electrically more resistive load than the 2.4, but its absolute impedance is lower, therefore requiring more current. Jim was expert at weighing the interlocking trade-offs to arrive at an optimized system functioning. But each system has its quirks.
All those factors are pretty subtle compared to how much piston is pushing how much air to produce how much bass before bottoming or running out of juice. That bass magnitude factor is the hard limit of each model format. 2.4 more nimble, 3.7 more authoritative.
Another ugly part of bass is that deeper bass, especially when louder, triggers room resonance modes. Deep bass causes problems which can overwhelm that extra few cycles of extension or visceral impact. All things considered, I would personally pursue (if I were in a position to pursue) a sealed bass solution which rolls off more slowly than ports. Reduced amplitude bass is still audible and can add musical foundation while exciting fewer room resonances and harboring less phase shift. CS3.5 lovers come to mind. But the cost of an additional crossover and driver in place of a passive radiator is far from trivial. That's where the well-integrated subwoofer comes to play. A Thiel sub with present-day high-performance class D or H or Benchmark-type THX amp could be very nice. I like Vandersteen's built-in subwoofer - serious cost of entry.
A slice of Thiel history is that we developed a huge folded horn woofer before we developed any salable product. I think I outlined it previously. We were all tuned into the importance of the bass foundation and how the musical harmonic structure develops from the fundamental. But pulling it off within our chosen price constraints was another matter entirely. Also the prototype powered speakers, which I mentioned months ago, produced sub 30 Hz bass with its own woofer-dedicated internal amp. But amplified speakers were unfeasible for us, especially when starting out in the late 70s.
Here's a speculation which I will try to confirm or refute over time: I suspect that Jim's final 7.3 project would have incorporated a smaller-diameter midrange section into the wavy driver, since it crosses to a 6.5"lower midrange. That smaller coax would have been the natural midrange for the 2.5 - remaining consistent with the model development protocol established over the years.
