A crosssover is not a cliff, so other fundamentals of slightly higher frequencies, lets pick 80hz (at progressively diminishing volumes) are simultaneously originating from the sub’s location, and each fundamental brings it’s own set of harmonics, 160, 240, 320, ..... ALL lower in volume, yet ALL higher frequencies, ALL becoming progressively narrower, more directional....
When the ear can locate a harmonic’s location, the brain can ’find’ the origin of the fundamental.
Near crossover points, and as frequencies transcend, you can have both the sub’s cone, and the main’s woofer’s cone both making the same fundamental and series of harmonics. To retain directionality, to get the benefit of imaging, it is better to locate a stereo pair of front firing subs adjacent to the mains. I don’t llike ports, if so, also front firing to preserve/enhance imaging.
My speakers have 15" woofers with monster magnets, to both move and stop the cone (they weigh 37 lbs each) I think of them as built-in subs. People with true subs and sub arrays certainly have more lows than me, but I benefit from the bass imaging they create.