Excellent job - better than mine, for sure, although mine are in the A-pillars not the mirror backing.
About imaging - I'm sure other pro's can describe this better, but I'll try to be brief.
The biggest struggle as a car audio SQ enthusiast is creating the illusion of a larger "sound stage" than you have to work with. The "sound stage" is where your brain imagines the sounds are actually coming from - now in my home system (Fultron Premiers from the late 70s), I have a physical 8 ft separation between my tweeters , which are about 12 ft from me, pointed directly at my head, with sound absorbtion above, below, and behind me - this makes for a fantastic soundstage, as voices seem to be coming from anywhere in between the speakers. In a car, your physical distance from the speakers is much MUCH less, and the speakers are much closer together. To create the illusion of a larger soundstage, you have to play tricks on your brain, hence "imaging".
When you look at car speaker tests, they do a frequency repsonse test for "on axis" and "off axis" response. On axis is usually described as between 0* and 30* (* = degrees) either direction from "pointed directly at you". Most car audio speakers (tweeters especially) are designed to not only sound great on axis, but off axis as well, as many factory locations are not ideal.
Now, frequency response and overall imaging impression are two different entities - flat on-axis frequency response does not guarantee good imaging, and generally makes voices sound like they're coming from your tweeters, about 2 ft from you. Very accurate, but sounds too "small".
Big sound comes from either running a time delay on your closest speakers, so the sound "seems" like its coming from the distance of your furthers speaker, or actually bouncing the sound off something like a windshield (like my CDTs do). This has the opportunity to loose accuracy, but sounds much more "acoustic"/"real"/better.
Basically, when someone asks "how's the imaging", they want to know... a] how accurate does it sound, but more importantly... b] where does it sound like the voices are coming from/how "big" is the sound.
Talk to your local SQ champs, and they'll go on for days about how to get better imaging/a bigger soundstage in your car, as well as probably turning my little description here into swiss cheese //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif