One thing to check is to make sure the rear end of the fender is the closest the fender gets to the wheel.
If the fender is further from the wheel there, snow (or other debris) can be carried up by the wheel and then get wedged as the fender comes closer to the wheel.
If the fender is close to the wheel there, anything coming up that could get wedged won't be able to get in the space and anything that gets in the space can be carried through to clear the wheel.
Ideally, you have a very slowly increasing distance from the wheel to the fender with the widest point being at the front of the fender.
And, if you get it juuust right....