You are not placing any sound deadener/reducing material in the door area while you are there?
I thought you are experienced in building some sound equipment? Quote=
"I used to build home loudspeakers back in the early 2,000".
The sound will badly reflect off the door cavity making even the best speakers sound like cheap replacement speakers. And all you will do is go crazy with your EQ or Sound Processor (best) to compensate. Audio car systems while have some similar traits to home sound system but the everchanging environment and setting up a vehicles sound system is really IMHO based on doing both professionally vastly different.
I owned and operated an Auto Sound sales and service store in the 80's.

Just saying before you rip on my response. I am only attempting to give suggestion and advise.
You also need to get the Tweeters high up and point towards the driver and front passenger generally in the pillars. In the door tends to cancel out some sound quality attempting to achieve. You can install tweeters in both area's which will complement the highs very nicely.