Sorry, But I feel I must point out that the Hucho Car and Civic are very different due to the transition radius at the top of the back glass. It is a Very Significant change, I really don't think they have much in common. I am noticing people don't seem to take this radius into account when considering their aerodynamic performance ideas, it is all just Angles, when indeed the radius makes a big difference as well.
I measured the Honda angles just the same, the back glass itself is at 19°, the top of back glass to trunk lid rear edge is 16°.
Again, the huge radius really helps to pull the air down in a smooth controlled fashion, but still, because it is "Sub-Template", it is pulling the air too hard there by reducing it's optimization.
The short Kamm is really messing things up IMO, you can see the tufts close to the top in front are angled up a lot, you really don't want that. Also the tufts on the trailing edge are pointed out. This looks to me like you have set up a tornado like vortex which is killing any kind of drag reduction you were hoping to achieve here. You need to do a full Kamm on this car, with radius side edges, or do nothing, it is already a fairly optimized shape and anything you put on that's half-baked will only create drag.
You really need to do ABA coast down testing on a flat or a hill to see whether it is making a difference, the tufts while helpful in visualization of what the air might be doing, is still a shot in the dark guess as to if there is any improvement.