The Scirroco is extreme to cover the wheels and tires. A normal eyebrow trim tapers out at the bottom, but if it was no wider than necessary but extends downward and in, in a similar manner, it would be more effective.
The box cavity is certainly more discrete that a full boat tail and
is can be almost as effective. Many people wouldn't even see it because as they say 'the eye cannot see what the mind does not know'. Excepting those darned novelty seekers.
There's only so much you can do to the visible parts, they didn't leave a lot of low-hanging fruit.
The parts not visible are the underside and the engine bay. You can make as much difference there as on the outside. Generally, a smooth underbody is better than an airdam, but much more work. Air curtains are one opportunity. For the engine bay a thermostatically operated radiator block or outlet vent reduces drag. Then you get into 4-into-2-into-1 anti-reverionary headers and on down the rabbit hole.
I won't drop names but there are extremely knowledgeable people here, I just repeat stuff I've heard. My VW is stock except for the stance.