To put in some of my own experience....the other thing that has to be understood is that fiberglass and composite products have a certain degree of sensitivity to climate differences. Fiberglass CAN warp/shrink/expand/etc. so it's going to be different on every car. It also has a bit to do with how your car went together from the factory, ever take out a bolt where your fender mounts? you can move your fenders in or our almost a half inch from where the bolt is centered in the mounting holes.....and every car has different tolerances from assembly. I bet if you pushed your fenders out a little bit the effect on the amount of flair the bumper has would be exponential. I.E. open up the gap between the hood and fender maybe a 1/16th to an 1/8" and see if it still flares out 2.5" as you say.
My majorly huge hand-made Focus RS replica build: http://www.focusfanatics.com/forum/showthread.php?t=289061
My RS conversion is For Sale: http://www.focusfanatics.com/forum/vehicles-sale/578185-sale-rs-mk1-conversion-2003-focus-svt.html