The bummer with the in door installation is now you need to go in there and unplug the mids to listen to just the tweeters. Curious if the sibilance follows them or the mid. Then you need to start swapping phase in every combination. First just the tweeters playing alone, then the mids alone, then all together in ALL combinations. I'd adjust everything to flat first....
I'd seriously contemplate removing the crossovers from the doors and putting them where you can reach them. Serious pain in the ass to swap things back and forth a ton and put the door back on. You CANNOT do these tests with the door open, you need the whole car as it will be as you drive.