A reservation for a DB engine and license model that is eligible for size-flexibility (MySQL, MariaDB, PostgreSQL, Amazon Aurora, or Oracle "Bring Your Own License") will automatically apply to a running DB instance of any size within the same instance family (e.g. M4, T2, or R3) for the same database engine and Region. In addition, the reservation will also apply to DB instances running in either Single-AZ or Multi-AZ deployment options.