I can’t believe no on mention this. Asura have flying city. They can build flying constructs. Who could possibly stop them from building some kind of flying fortress, armed in heavy cannons? No on could reach them. Invasion from above. With that, distance wouldn’t be problem, even without gates.
Setting few flying outposts in strategic point in the world would be nice idea. Taking over mines, cutting enemy from supplies.
I think we have a winner.
Of course, everything depends on how fast these construct could be build.