Not seeing the sound

In addition to chayro's description of a phase issue, you most likely will experience a loss of bass impact. If all the instruments/musicians are positioned in the right place and your imaging has width and depth with good dynamics, then you have found your soundstage.

The sound is quite 3D now. There’s width, height and depth, if that makes any sense.

Yup, that’s it. As stated above, the speakers have disappeared.
You should also now hear quite a difference between many digitally remastered (compressed) recordings and the original versions. The original will have depth and space between instruments, e.g., the singer will be forward and center, while the drum kit will be located at the back of the soundstage.

When I achieved this desired quality in my system, I stopped buying compressed remasters and went looking for the original CD's. This applies mainly to Rock and I now shop for music on Discogs.

I think there are other members who have not found their optimal speaker placement. When I look at some of the "Systems" photos, there’s no way some of the speakers are placed in an ideal position.
It took me weeks to get it right when I bought new speakers.