The air nozzles position depends entirely where the sector gear stops. In full auto it can be random, in semi it can be in a different place on every gun. The only thing that matters is that it visibly goes back and forth every shot.
Misfeeding can be due to the rubber, but also check the tappet plate.
Sounds like the flat hop was done wrong, or they didn't use a soft enough nub for it. Flat hops especially should never straight up jam a gun when you overhop a little bit, they're designed to spread the contact over double the length, so you should be able to get much more overhop with a flat hop than a conventional rubber.
I'd also argue the 70* rubber is too hard for a flat rubber. There's less wear on them to begin with by design, but you also need a softer material to impart more grip over the length of it.