[19bonestock88]

I think that the spoiler changes the effective rear glass angle, making the profile closer to the Kamm-back shape... If it also extends past the end of the trunk lid, it can also help with the fineness ratio... The one on my wife's Impreza isn't too tall, but it does extend past the trunk lid for nearly an inch, and Subaru chose to put them on all the 15-up models(even my wife's 2.0i base) for an improvement of (supposedly) up to 1mpg highway...

Which kinda straightens my perspective; I think my spoiler may end up too tall, so I might reshape the triangle reinforcements for a lower height and try to elongate the hypotenuse surface past the end of the trunk lid...