if the splitter is only for looks and attached to the lip only then whatever, but i hate to see mis-information in posts.
1. for the splitter to be functional (aero wise, reduce drag/create neg. lift) it doesn't need to extend to china. as long as it extends atleast to the back of the bumper (start of the wheel well) it will function.
2. it does NOT need to be strong enough to stand on, only strong enough to resist deflection at the speeds it's intended to see. some ALMS cars splitters may be strong enough to stand on, but the forces you encounter at 185mph to 200mph are much greater than forces @ 140-150. drag and wind forces rise exponentially to the rise in speed. also, many of those have bumpers and canards integrated with the splitter and need serious attachment hardware. the canards in particular produce downforce and drag like a wing unlike a splitter which creates net downforce/neg. lift.
3. a splitter does not need to be 3in. past the bumper to make a difference. although up to a point, the larger the better which is why some race classes have a maximum limit on length. or others like nasa tt (iirc) assign more points depending on the length of the splitter.
even though my splitter is only 2.5'' long and doesn't extend past the back of the bumper, i can tell you without a doubt, the splitter i made makes a big difference in stability at higher speeds. i just recently went to a track that i had not driven since my splitter install, and the difference was incredible. where my cars steering was light and would wander above 105mph previously, it was now rock solid and planted up to 135mph+
actually, the difference can be felt even at highway speeds, especially in strong head or cross winds. while my aluminum splitter is very strong, i don't think i could stand on it, and honestly there isn't that much pressure pushing straight down on the splitter like that, even at the 140mph speeds i've reached at big tracks. a splitter isn't generating downforce in the same manner as a big wing would. it's main claim to fame is the reduction of drag and lift. reducing lift underneath is like adding downforce on top without the drag.
here's a few pics.
this is with an aluminum lip i made. painted it black later
without lip - rear attachment point (oem support rod bolt)
frt. attachment point. oem threaded hole/alum. strap (bent into L bracket) and some allthread. allows me to adjust angle, although you always want it horizontal anyway. 4 attachment points allow it to be removed in about 2mins. or so if needed.