According to Hybrid Audio PDF manuals, between 1 and 2KHz imaging is dependent on both the intensity (level) and distances. Above 2KHz, intensity is the most important factor for imaging. Getting the time alignment set up for the front stage is easy IMO. I personally suspect that getting the intensity right above 2KHz can be more difficult in a car. First, it's not just the tweeter that's playing audibly in that range. You probably need a good equalizer, experience, or a self tuning processor. As a start one easy trick to try is to turn down the level of the closest tweeter by about 1 to 2dB. This can result in in-audible change in frequency response, but imaging can be more consistent. I used to do this before I got Pioneer DEH-80PRS with HAT Imagine speakers. Once I got the DEH-80PRS, I let it do its auto tune thing, and while the low end needed additional tuning, I felt like the resulting midrange and high frequencies imaged pretty well, tonality was also good. The sound is neutral or perhaps a little up front, which I like more. Could the L1 tweeter be worse than the Imagine tweeter in this respect?
Also I suspect that with hybrid audio tweeter you need to do some work on equalization in the 2-5KHz region. A typical 6.5 woofer installed 30 degrees off axis or more will not give you good dispersion of sound above 2KHz, but a HAT tweeter like L1 probably does not like playing below 5KHz. If you leave it as is, this may result in a too "laid back" sound. Some people like it. I don't.