Very strange indeed. This is the one I got from JDMland. It came in the set of JDM FG2 Civic 06 + Si Coupe front and rear red 'H' combo pack. The rear fit perfectly
The only thing I can think of is where your mount of it is. On an EX it fits right under the lip spoiler, in the Si picture that Exin posted, it appears to be a bit lower down the trunk lid. Perhaps that's why there is more of a curve at that point.