This grouping is supported by both Robert Blust and Paul Jen-kuei Li.

Li considers the Siraya-speaking area in the southwestern plains of Taiwan to be the most likely homeland of the East Formosan speakers, where they then spread to the eastern coast of Taiwan and gradually migrated to the area of modern-day Taipei.

[1] Luilang is often lumped together with the Ketagalan dialect of Basay, but is poorly attested and remains unclassified.

[2] Li[1] presents the following criteria as evidence for an East Formosan subgrouping.

Li[1] also lists dozens of lexical innovations shared by the East Formosan languages.