This. There are many biomes not having any invasion forces, and some have only very limited possible armies.
It would be much more fun if player can get hunt down regardless where he is as long as he reaches certain low alignment, say -200.
A rare chance invasion will spawn near player, and the army will be a faction that has low alignment. To prevent player with many enemies get endless invasions, a cooldown should be in place after each such invasion takes place (the cool down does not affect biome-spawned or horn-spawned invasions).
And no this would not break immersion/lore, if Nazgul can go to bree and united army can go to eye of mordor, an elite regiment should be able to go anywhere to hunt down a target