My plan is to add side panels eventually (something like
this that I posted earlier, but I'm probably going to forego the side skirts) to make it more of a box cavity than a mere trunklid extension. Again I do want to test it, but that'll have to be after the whole O2 sensor thing is resolved.
My extension extends further back than yours, so that probably helps. And if I can get VGs to work (big
IF there lol) the benefit should be more noticeable. It's more for air over the tip to attach and have a smaller rear area than an actual box cavity effect, yet. I haven't read anywhere of it hurting and several people have seen a benefit, so I guess we'll see.
You're making me doubt myself now lol. How am I supposed to improve aerodynamics at the rear without going for a crazy boattail since a kammback won't really help my sedan??