As he expected, the front fender appeared to reduce wind resistance. He used a telescoping fender to test the effect of length. I plot the result here: "N" corresponds to no fender, "S" for short, "M" for medium length, "L" for long, "XL" for extra-long, and "MF" for a mud-flap on an extra-long fender.
There appears to be an optimal length: the fender blocks the wind from entering the brake area, then going longer than that is counter-productive.
Jan dismisses the effect as relatively small. However, ignoring his "repeatability" tests to establish error bars, I'll plot the naked numbers of the difference in CdA from the fenders to the difference in CdA reported by Scott for "aero" mass-start bike frames relative to a "round-tube" frame, my guess the long-head-tubed Scott CR1. Scott's tests were with a dummy mounted on the bike. Jan's tests were with a rendered outline on a display against which is aligned an image of his body for repeatability when conducting the wind tunnel tests. I use the zero-yaw data from the Scott test since that is how the fender test was done.
Curiously, the short front fender seems to offer a greater advantage than the Cervelo and Felt, and not much less than the Scott Foil. Velo Orange fenders cost around $60. The Scott Foil frame is probably around $3500.