If you take a look at the installed product picture in Jim Carter's ad for FP124, it looks like the welting stops at the point where the fender and front of the cab cowl meet. That's what I have seen on many AD series Truck/Burbs/Panels anyhow.
Craig,
That's about where mine stops, at the end of the cowl, looks to be about 1/8 short but its 5 yrs old and not sure if it shrinks or not.