I haven't gotten to the 4 foot kamm, mostly because of financial constraints. I'd need to get a clear plastic sheet for rear visibility and find suitable supports. It would also eliminate the use of the trunk, which I'm trying to avoid.
With some rough eyeballing, it looks like a 15" flat spoiler on my car would make about a 15* angle from the roof, and the vertical plates on the sides could give the effect of extending the boattailing. The 15" extension is short enough for me to reach the lock on the trunk and open it
I'm going to do some more research on flat spoilers before I cut up more coroplast and test.
Here's some more shots of the Fusion:
