I had a go with heat shrink wrap for only the small triangle back there as well like this and didn't really notice and aero improvements nor did I like the way it looked so I removed it. It was probably partly because the way I did it made it look very plain, but I've seen others that looked way better. As for effectiveness, it would probably would have been more aero if it was stopping the wind from hitting the spokes at the top of the wheel like yours did in the last pic.
To get my CdA back to respectable levels I removed the canvas style seat bag (top pic) that's been on my V20 the longest and replaced it with the small pointy fiberglass seat cowl for yesterday's ride (middle pic). I also moved the head rest bars out a little and tilted them back so that my head is laid back a little more than usual. During the ride I felt a little too stretched out and having to reach for the pedals a bit so before the next ride I am going to slide the BB closer about 1cm or so.
For the past few months I have been increasing my FTP and power at 1 minute, 5 minutes and 10 minutes little by little. However, I have been focusing on it so much that I can't say I enjoyed my rides like I usually did. So, when I move the BB I am also going to remove the 53/39t Shimano 105 cranks with the power meter and put the 54/40 Dura Ace cranks back on. I'll lose the PM data but I'll be happy to just enjoy the rides again.
The other day, I went to a recycle motorcycle/bike shop that I got the seat cowl from, and they had another one, new, fiberglass and in flat white for I think ¥12,000. I didn't get a pic of it, but it is the exact same as the one in the middle pic.
Yesterday's ride with all of the adjustments at 0.195 CdA.
