I thought they said the reason Hingashi hadn't been invaded by the Empire was because they wanted to finish conquering the Three Great Continents (Aldenard, Ilsabard, and Othard) before they started going after outlying territories? Between that, their relatively weak navy, and their airships requiring refueling for long-distance travel, I have a very hard time believing the Empire's reach extended to Tural.
I hate to say "Citation needed," but...