What realm they are attained in

The results of Stream-Enterer, Once-Returner, and Non-Returner are exclusively actualised on a Desire Realm support:

• The first two and Gradualist Non-Returners: because their approachers are pervaded by not having attained an actual concentration.
• Leaper Non-Returners: because the physical support for attaining it is the same as for the new arising of the path of seeing (same lifetime) and there is no direct and new arising of the path of seeing on an Upper Realm support.

The result of Foe-Destroyer can be actualised on the support of any of the three realms:

• Desire Realm: e.g. Simultaneous Abandoner Stream-Enterer
• Form Realm: e.g. some Non-Returners proceeding to the Form Realm
• Formless Realm: e.g. Non-Returners proceeding to the Formless Realm

See: Abhidharmakosha

Up a level: Results of the Way of the Śramaṇa