I'm wondering if there is available such a rear spoiler for GK, which instead of increasing downforce or reducing the drag is intended for leding the airflow from roof to rear window to reduce the hatchback-typical tendency of the rear window getting dirty i.e. to interfere the trailing vortex raising the dust and spray to rear of the vehicle. Such spoilers have been used in 80's in STWs and vans.

 

https://www.mooneyesusa.com/product-p/aa740.htm

Try these.

 

But those are more made for old school designed cars with no upper rear spoiler. Not sure how well they would work on a Fit.