Consider, fenders aren't just for you. I had a set of fenders on my rain bike last year that didn't quite come halfway down the rear tire. This resulted in a nice Oregon racing stripe up my back on a regular basis. Since I was riding in the rain anyway, I justed accepted this.

Then one day as I was stopped at a traffic light, a guy who had been riding behind me commented (quite nicely, all things considered) on my fenders being too short as he picked some of the bigger pebbles I had flung at him off the front of his jersey. Now I have better fenders.