Dual subs integrate best (sonically invisible) when they are used in a left-right configuration.

If you sharply restrict output over 80Hz. dual subs can also be placed on the same side of the room where they will still be sonically invisible almost 100% 0f the time.

Whether dual subs are connected as stereo or mono subs barely matters as few studio recordings (two-channel) have stereo bass content. Some classical recordings made in large venues may have audible stereo hall ambience.

If you sit half way between the side walls of a room, the bass frequency response from a pair of subwoofers on the same side of the room will usually be better than using
left-right subwoofers.

I personally use one mono subwoofer just to the outside of my left speaker for two-channel audio. My crossover and parametric EQ allow me to sharply restrict output over 80Hz. so no male voices can be heard through my subwoofer when the other speakers are turned off.