I'm running 37mm PDW Road Plus Fenders over 32mm Compass tires, which probably measure a little under 32mm. I know, crazy--but they work just fine. I don't know if it's the shape of the PDW fenders or what, but they just work. They did take a while to install, because the margin of error is much smaller than with bigger fenders.
I also have 45mm Planet Bike Cascadia ALX fenders over 35mm Paselas on another bike, and those seem to redirect water right onto my toes. So who knows?