The goatheads have a lug attached behind the point. And all the thorns max out at a certain length (I am not going to give you the length in millimeter, simply pick some up off the ground and inspect yourself). The lug plus the thickness of the thorn at the base stops them going beyond a certain distance in the tube. This distance is long enough to puncture any standard thickness tube, but not long enough (when used in conjunction with Armadillo tires) to puncture a thorn resistant tube. I have literally pulled and inspected hundreds of tubes and Armadillo tires in goatweed country and the picture is always the same: the tip of the thorns project only about 1-2mm past the material of the tire. The tips are stopped from going any further by the thickness of the base of the thorn. And eventually those tips either break off or becoming blunted by vibration/movement against the rubber of the thick inner tube.

So the answer is: yes, no matter the small differences in the length of the thorns, the ones that penetrate always max out at a certain 1-2mm distance beyond the material of the Armadillo.

And since you ask how. . . . The answer is because the Armadillo utilizes two densely woven layers nylon that do the actual flat protection. Imagine you have a steel chain link fence, two layers thick. Now imagine you try to push the tip of a plastic funnel (such as you might use to refill your lawmower) through those two layers of steel chain link. The tip of the funnel is only going to penetrate so far. Since goatweed thorns absolute maximum length pretty much is the same everywhere, the visible thorn tips that you see penetrating inside your Armadillo tires stick out pretty much uninformly about 1-2mm, unless the tips have already broken off or they are still working their way in.

So that's the how. Put that in your pipe and smoke it. Or do your own research. Actually goatweed consumption is supposed to be good for virility and restoring hair loss, so it could do you some good. Alright -- just kiddin big guy! ;-)