The Liao did not treat the Han Chinese as equals, so the more their numbers grew in proportion to that of the Khitan, the more the ruling class would keep a closer watch over them. You also have to realize that the ruling class feared assimilation to the point where they attempted to deny the Han Chinese certain rights from the foundation of the dynasty, and opposed Abaoji's policies towards them, so the court would probably enact harsher policies if they felt that it was necessary.