Today I rode home from work after a rain (NYC has been rather like what NYCers imagine London to be like lately…) after stowing my Stida on its rack instead of propped against a wall, in order to bend the mudflap as StridaD suggested.
Result? No spray. I think this is the problem. Certainly my Brompton has a floppy front mudflap that points downward but the rear mudflap is firm and parallel to the ground.