Forgot to include this: One area in which a vertical array of multiple small woofers has superior room interaction relative to a single large woofer is in the floor-bounce dip. The multiple small woofers will have their floor-bounce dips at different frequencies and so they will tend to fill in for one another. The single large woofer won’t get that benefit, though its dip will be smeared out a bit compared to a single small woofer, and therefore will be slightly less deep. The ear/brain system is fairly forgiving of the floor bounce dip because it occurs naturally all the time, but minimizing it is still beneficial.
Duke