I just perused
James' review of the S7T, paying close attention to the bass measurements and some of the design choices Perlisten went with. You should too, as I think it may address your questions.
Measurements of what they're doing in your room would be elucidating, but we can make a few guesses as to what's going on in your room.
Note the shallow, very gradual 1st order-ish roll-off below 100hz. As James noted in his review, this was intentional, as such an anechoic response tends to play well once the speaker gets plopped within a room, as they'll get some boundary and/or pressure vessel gain.
Also note the port tuning (the saddle in the impedance graph) which is way down in the mid 20hz area. Ported speakers don't get much in the way of boundary or cabin gain below port tuning, but they can fully capitalize on it above port tuning. The port tuning being so low gives you everything above the low 20's to play with, as far as boundary/cabin gain goes. You can eq freq above port resonance too.
So the S7T seems to be a kinda sorta overdamped low-tuned reflex approach, one that's essentially full range. It's a recipe for tight, dry, highly resolving and realistic bass. Speakers with more flat and deep anechoic response can sound too thick, too phat, and less resolving and realistic, once the room gets it's ugly mitts on things. Perlisten made excellent design choices here.
I think those S7T would be right up TLS' alley, guessing by the sort of bass he prefers as expressed here. I hope he's able to drop in on you. He can directly answer your questions, and might find another commercial speaker he actually likes. (He did give a thumbs up to fellow Minnesotan Squishman's KEFs, which also have a shelved down deep bass response, but Perlisten did it better.)
Your room is fairly large, so I can't imagine you get much if any cabin gain, but you will get boundary gain. Closer proximity to walls and corners will boost lower frequencies. That's what you're hearing, and as you have experienced first hand, placement can be a powerful (and free!) calibration tool.
I'm less convinced now that you *need* subs. I would give a qualified "Maybe", to address modal smoothing or get more spl perhaps. Neither of those needs are demonstrated.