Non-exclusivity
The overlord-tributary relationship was not necessarily exclusive. A state in border areas might pay tribute to two or three stronger powers. The tributary ruler could then play the stronger powers off against each other in order to minimise interference by either one, while for the major powers the tributaries served as a buffer zone to prevent direct conflict between them. For example the Malay kingdoms in Malay Peninsula earlier were the subject to Srivijayan mandala, and in later period contested by either Ayutthaya mandala in north and Majapahit mandala in south, before finally gain its own gravity during Malacca Sultanate.
Read more about this topic: Mandala (Southeast Asian Political Model)