Mine's closer than a 1/4" per side. But the fiberglass version off of eBay is a little shorter than the originals are. The original DC spoiler I have goes all the way out to the edge of the deck lid, the fiberglass copy is probably an 1/8" or so off the edge. Enough to be noticeable.
The fiberglass version seems to have squared off the sides a little more, the original version tapers all the way down from the top to the sides, the fiberglass copy tapers down but then has a vertical edge on the sides. Since it is just fiberglass you could do some work on the edges, just fill out that last little bit of the sides so that they're tapered instead of squared off.
