Nice work. A few of us now have tested this general Civic body type and have seen some similar things.
Here is a pic of tufts on my car, pasted in place by a light water mist that was on the car when I drove off:
Notice the recirculation zone near the base of the glass at the center that crosses onto the trunk. I think we see that in your #3 video too. And the pattern of evaporation of mist on my car in the below photo also suggests a recirculation zone in the same place:
Someone else on here has also recently made similar tests.
I think you have success displayed in these vids. Attached flow behind the rear wheels and probably better attached flow off the tail of the trunk with cleaner separation because of the extension, which I'm told is better.