"Everyone knows that an X block can be used to block a front kick"? Hmm, I am guessing you are quite young as I cannot really imagine an adult using the "everybody knows" line to support their contention without any other comment. And there was I thinking that interpretation of karate movements was a complicated matter with many possible, plausible outcomes...
My experience is that x block has only ever worked in single attack sparring where the front kick is called first and no punch follows the kick. This kind of prepared sparring is popular in Shotokan clubs as a basic training aid and from memory in some Shito clubs (I trained for a while in the mid/late '80s in a Tani Ha Shito Ryu club in Manchester.)
In 25 years of free sparring I have never seen anyone use it against me or anyone else. Putting you head at your attacker's waist level even for the happy if remote possibility of damaging his shin is probably not a sensible tactic if your life is on the line.
I tend to go with the Ed's suggestion that breaking the trunk or whatever it is called using crouching x block, is an imported sword principle. Cutting someone's leg off with a sword ends the fight, hitting the shin with the fist does not. Meanwhile you are off balance and getting hit in the face.
Since the bunkai theory I observed in a Shito club (granted only one but with a Sandan instructor of British team fame) was as poor as your then average Shotokan club, I am suspecting that Shito Ryu may have no more idea of kata interpretation than mainstream Shotokan.
There are several possible meanings to x block (certainly not just the knee in the attacker's ribs/neck whilst choking someone as an ending to throws I mentioned) depending on what precedes it in the kata-why not read the previous pages you ignored and you might see that many possibilities have already been discussed, including the front kick one you are introducing as if a novelty.