Jyden, I looked through your album and I like what you've done so far.
Judging from one of the pics, your kammback/roof extension looks short. I know the Yaris' rear is very steep, so the kammie can't be 50cm long, but you should extend it to the end of the rear bumper. This will give the airflow a few more cm to stablize, and it will make the wake area slightly smaller. I would have made mine longer, but I'm not sure about legal issues (things sticking out beyond the car's natural dimensions). And remember that sides should also close in at the same angle!
More pictures in my modding thread, page 3.
BTW: Have you thought about removing those window shades? I doubt they help airflow.
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e·co·mod·ding: the art of turning vehicles into what they should be
What matters is
where you're going, not
how fast.
"... we humans tend to screw up everything that's good enough as it is...or everything that we're attracted to, we love to go and defile it." - Chris Cornell
[Old] Piwoslaw's Peugeot 307sw modding thread