as modeled into this configuration for me by
the intent was to "help" more into the 35 ish to 90 ish range as a unit actually firing forward into the room, as the other subs are either even with or actually in back of the MLP, firing forward. i.e. "punch"
MAX is actually sitting nearfield about <4 ft behind me.
The fusion 15's very smooth and even as "small", XT32 set an xo of 40, totally adequate as stereo/ 2 channel listening, even without the subs (but except for a "test", never again, unless by request).. (think "Phantom of the Opera Remix" fine trouncing ditty
the 24" got shoved into the mancave , <110ft^2, after building the 2 x 30".
I think my over all 5Kft^3 house volume was just too much for 1 lonely THTLP
remembering that a larger THTLP is about a smoother and slightly deeper response, the 2 in my LR , sitting butt to butt each had the prescribed loading of 18" in a 14.5 wide room behind me.. shaken and stirred . . .and only EQ'd with YPAO (older 663) thru 2 x BASH 300's. iirc my 818 had an "on" relay issue since fixed ,free, and currently running the Scatmos right side tops.
While I'm currently trying to manage EQ all 4 subs thru the new minidsp 2 x 4HD, I can tomorrow put the whole thing in Stereo, turn down the gains for the 3 larger subs and see what things sound like.
The 24" never got to play with the F15's
based on the opinions of others, I'd venture to say that given a more adventurous attempt at placement and usage of REW wrt EQ, either with XT32, the Inuke Dsp controls or now thru the HD unit, that fact that the sub can take about 1K wattage makes me think, it should well kick down the walls and eat the THTLP's lunch
even a BASH 300 is way too much for a THTLP.
as for using science to discuss the mutual or exclusive benefit of an FLH vs, Ported, way above my paygrade
and the room. placement and all that, lots of variables
given that the original VBSS can be managed to get appreciably below 20, I'd be inclined to say that for the money and time to build either a THTLP (1/2" ply requires attentive craftsmanship, I think the driver as $280 ish)or 2 of the VBSS, 3/4 ply and a buttload of Kreg screws and drivers at <$100 each, an Inuke3000DSP
and 2 subs for room modes, placement options, all of that.
obviously I'm a bit behind the learning curve but I listen well