In this case this is done by Jan Heine for aerodynamics, not splatter reduction.


short excerpt
That’s where the Rene Herse’s fender fairings come in. (They may look like shortened fenders, but they are not intended to keep the rider dry.) By shielding the tops of the tires from the airstream, they reduce the wind resistance. Now the airstream is hitting the fender fairing—which moves at 36 mph—rather than the tire at 72 mph. We optimized the shape of these fender fairings in the wind tunnel, until they decreased air resistance by 1-2%—almost as much as a set of aero wheels on a racing bike. In road racing, fairings are illegal, but these rules don’t apply to most gravel races.

full link https://www.renehersecycles.com/aero...-gravel-bikes/

may be of interest
https://www.renehersecycles.com/spec...xl-rene-herse/


https://www.renehersecycles.com/oreg...od-or-madness/