They should not be that long. Here is a link to my Trumpeter P-40B with Eagle Edition decals on it. Notice that the back edge of the mouth is not near the wing root. They do fold slightly over the edge of the intake unter the nose though.
There are some links at the bottom of that page that show several pictures of the original Tigers. Keep in mind that the markings on the planes were nto exactly the same. Different planes had the mouth slightly different, and it seems like the differences among the three squadrons was pretty significant. It could be that the decals you have are for a different squadron and they should go all the way to the wing root.