My experience is that whether or not a speaker disappears is dependent on room acoustics, location of the speaker in the room and on the remainder of the system. Any one of these facotors may limit the ability of the speaker to disappear. Similarly, these factors will effect the ability of a speaker to image beyond its outside edge. Having said this, some speakers are obviously better in this than others. The best examples that I have heard are small stand mounted two ways, point sources like the Quads and planar drivers like the Magnepans and Martin Logans.
A related issue that is also revealing of the quality of the system as a whole is where the system places noise. Much of my listening is analog. In a really good system the record noise is localized on the front of the speaker and is not a part of the soundfield. In lesser systems the noise meshes with the sound field. A related phenomena is the ability to move around in the room and have the location of instruments remain stable. For many years, I thought that this was solely an artifact of the speakers and their set-up and that it was impossible to have a sharply focused image and not have it collapse as one moved away from the ideal listening position. Now I am beginning to think that this may be an artefact of the phase accuracy of teh system as a whole. Given phase accurate speakers and electronics it is possible to have sharp image focus which is stable with movement away from the listening position. I had previously experienced this with Beveridge speakers many years ago, but not since until recently.
A related issue that is also revealing of the quality of the system as a whole is where the system places noise. Much of my listening is analog. In a really good system the record noise is localized on the front of the speaker and is not a part of the soundfield. In lesser systems the noise meshes with the sound field. A related phenomena is the ability to move around in the room and have the location of instruments remain stable. For many years, I thought that this was solely an artifact of the speakers and their set-up and that it was impossible to have a sharply focused image and not have it collapse as one moved away from the ideal listening position. Now I am beginning to think that this may be an artefact of the phase accuracy of teh system as a whole. Given phase accurate speakers and electronics it is possible to have sharp image focus which is stable with movement away from the listening position. I had previously experienced this with Beveridge speakers many years ago, but not since until recently.