Imaging/staging refers to the positioning of all the instruments, for example, if a singer's recorded directly in the middle of the stage, then your system should reproduce her voice coming from the center of your dash, at somewhere close to eye/ear level. Likewise, if a certain instrument is miked to one of the extremes of the stage, then the system should reproduce that realistically.
The problem you have with coaxials, is that mounting them in doors tends to drop the stage height a lot, because high frequencies are more directional than lower frequencies and you're way off-axis of the tweeters. What components let you do is mount the tweeters in such a way that your staging cues are preserved, such as on the A-pillars or upfiring in the dash.