How come air units cause two drones even if they're in the home base?
All offensive air units are considered out of territory no matter where they are. BUT this does not apply to defensive air units like interceptors (planes/choppers with the air superiority ability). See this article for more info: http://alphacentauri2.info/index.php?action=articles;sa=view;article=33
If I remember correctly, some unit types (apparently including air units) don't count as being home for the purposes of police duty. I cannot remember whether this applies to copters, but I seem to remember it applies to needle jets.