I have absolutely no problem with this.
I do, which is that it's quite hard to justify the Realm just not knowing about the West, when they're the direct inheritors of a world-spanning state that
absolutely included the West.
The Realm should have ancient maps, tax records, ocean charts, autobiographies – hell, the Scarlet Empress is technically
from the Shogunate. Presumably she targeted raksha in the West with the Sword of Creation, too. Even without her, you've got things like bound demons or divine contacts or sorcerous scrying or Bronze Faction Sidereals which can very easily reveal "land in that direction, yo", not to mention the idea of it taking 500 years to discover the West when 20% of your ruling caste are amazing sailors and your navy is the best in the world.
If you want to do this, I'd advise something I rarely do, which is a New Plot Event. Namely, the use of the Realm Defence Grid in the West caused a total elemental shitstorm post-Contagion, which left the passage to the West essentially unnavigable in anything approaching safety up until about a century ago, when it finally and slowly started to die down. Call it the Typhon.
The Terrestrial Bureaucracy in the region is a post-apocalyptic mess ruled by raksha pirates and elemental thugs, the Storm Mothers have gone totally off-reservation and unionized for more storms, longer storms, and storm overtime, the Lintha use powerful demon vessels to move freely through the Typhon, which is how they've survived so long. The few little empires of the West cognizant of their likely fate watch nervously as the steadily-opening opportunities represented by the fading storm cause the Great Houses to chafe at the bit, with many of their disputed territory claims left unresolved at the time at the time of the Empress' disappearance, as further catalyst for political jockeying and internecine warfare.
You've got to do something like that, and then juice it for all the fun it's worth.
"It's really far away tho", doesn't cut it.
Meanwhile, the Realm is held out of the far North by the climate and logistic problems but dominates the more temperate regions, and the South has come to accommodations with the Realm, maintaining a degree of independence and their lords pay their tribute to the Realm but maintain a lot of self-rule.
The deeper North and South are in an interesting position with regard to the Realm, because – like most real-world empires – their supply chains and long-term occupying capabilities look at endless tundra and scorching desert and say "haha, fuck no". On the other hand, stick a few Dragon-blooded with the right Survival Charms in there, and suddenly a march into Fucking Hotville or No Waterstan becomes damn near
simple. So they can't keep the outer South or North in a headlock, but they
can stab them with comparative ease – which is what they were expecting to do to the Bull, before he pulled like three whole other Solars out of his ass.