Good point. Cardiod doesn't always help. It would for me in my 3.5m square room!
Aside from max spl, I'm 100% sure I could not tell the difference between an 8351b and a 8361a on the w371a.
Well, strangely I heard slight differences between the 8361 and the 8351 both with the W371,though I'm not at all a golden ear guy at 70 years old (68 and when i listened to these two configurations).
With the 8361, the low medium was a slightly bit fuller but a bit too thick, with GLM calibration activated. The W371 isn't a pure sub, the cut off frequency overlap the main monitor in the high bass/low medium, where the 8361 has more weight and dynamic, so that maybe the reason for my impressions.
For acoustic music, the smaller 8351 had my preference. Of course, this is subjective, the perceived difference was marginal and possibly mind biaised (it wans't a blind comparison).
Both configurations were absolutely excellent and I could live super happy with any of them.
But I would have chosen the smaller 8351, all things taken into account :
1-sound preference as subtle as it was,
2- a lower price
3- a smaller size somehow more esthetic because the 8361 looks like a too big head above the W371.
Between the 8380, the 8361 and the 8361, I would choose the 8380 in a room bigger than mine and the 8361 in my room, and the smallest and a bit cheaper 8351 will be fine too.
Esthetically none is beautiful nor ugly, the big plain rectangular 8380 is finally the one I prefer.
I would definetely not buy the W371 -too expensive, too big and rather ugly, as good as it is.