What distinguishes ījāz al-qaṣr from ījāz al-ḥadhf?

Ījāz, Iṭnāb and Musāwāh: Concision, Ellipsis, Expansion and Equivalence

• Qaṣr has no required ellipsis; ḥadhf has a recoverable omitted element
• Qaṣr occurs only in poetry
• Ellipsis never has evidence
• Both are forms of repetition