Sam, a Tzamid Passil is with any substance that is Chotzetz from Tuma. Plastic is not a Keli, it might be Pshutei Keili, if it was a sheet and not a bag, and it might not be Mekabel Tuma at all, like Limey said.
The question I have is that an Ohel Zaruk is not an Ohel. We know this by a bird carrying Tuma, that it is not Maahil. Why don’t we apply the same to the Kohen himself, that he is not being Maahil on the Tuma.
As far as other places, this problem is only where we know for a fact that he is flying directly over Jewish graves.
Ad Larakiya is a good theorhetical discussion, sofar. There isn’t much to go by so we can’t really be Meikel with Dimyonos (???? ???? ????? ???? ????). But we can have fun speculating if the planet has a planetary Techum, perhaps a Mehalech of 500 years. This is 10 Parsa a day multiplied by 365*500. That’s 7,300,000 Mil, whatever that comes out to.
Another possibility is as long as you feel the pull of Earth’s gravity. Or perhaps from when you start to see the world as a Kadur. Maybe we can draw the line at the level where the rocket has to come at the critical angle, since that is like a layer, the Kipa.