I've wondered about this myself, how far do the flaps need to stick out to offer protection. I'm mainly concerned with just dirt, dirty water from puddles.
You could always get some urethane flaps and trim them to what you want. Leave the outer edge and bottom intact, and trim the inner edge so that everything people see still looks nice and clean. You'd have to re-drill the mounting holes, but you can just use your untrimmed flap for a template on the trimmed one, and then the first trimmed one as a template for the second.
That said, when I first put mine on they looked huge, and now I don't even notice them anymore.