Spent the weekend on my midrange install and it actually turned out clean

Did basicly the same thing in my S60 last fall and went through the exact same ring saga. My first set had the bolt circle off by about 2mm beacuse I measured the mounting flange with the driver sitting on top of it instead of underneath, so the screws bound up at an angle. Redid it with a pair of calipers and a spare gasket as a template and the second print was fine. I ended up mounting a set of Morel mids in there and the imaging change alone sold me on the whole job.

One thing I learned on mine: leave a little slack in that pigtail wire when you tuck it back. I zip tied mine too tight against the dash frame and over a Michigan winter the foam on the harness compressed just enough that I got an intermittent crackle in the left side. Reopened it and gave the loom a couple inches of free play and it's been quiet since.

On the thin lower mids, mine turned out to be less about the point and more about the slope. Once I took the low pass down gentler on the mids the punch came back without getting muddy. Might be worth trying both before you commit to moving the frequency much.

Funny reading this because I fought the same thin lower mids in my V70 for months and it turned out to be a mounting problem, not a DSP problem. My midrange drivers were bolted to a pair of MDF rings I cut by hand, and the rings were rigidly coupled to the dash structure. Every time the bass hit, the whole opening buzzed and it made everything below 200hz sound muddy and hollow. I stripped it back out, put a ring of closed cell foam tape between the driver flange and the bracket, and redid the screws with rubber grommets. The change was bigger than anything the tuning software gave me. Before you chase the crossover point, try pressing your palm flat on the dash trim while it plays at the volume where it gets thin. If the buzzing or harshness changes, you have a vibration issue and no amount of EQ will fix it cleanly. Also worth checking that the driver actually seals against the opening, since any gap between the back of the cone area and the dash cavity lets the sound leak and do wierd phase things behind the grille. Mine had a quarter inch of open space around one side because the printed flange sat slightly crooked, and a bead of butyl rope around the rim was the fix.

Not sold on the slope thing myself. I chased a thin spot around the same region in my last install and a gentler slope just smeared everything together instead of fixing it. What actually worked was knocking the mid level down a couple db right at the crossover and leaving the point alone. A gentle slope can hide a hole instead of filling it, wich is worse because it sounds fine solo and wrong in the mix. Worth checking with pink noise and an RTA app before assuming the filter shape is the culprit.