Im waving the BS flag. I used to commute home to MMMY via IAH weekly. They told me we couldn't do it some times. Ask them to print out the jumpseat guidance. It specifically states you cannot ride back in to the US jumpseating in the back. The example on the guidance is from mexico to the US. If you read after where it says OAL pilots are prohibited from jumpseating it states from outside the us back in. Hope this helps..