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

Ījāz al-Ḥadhf: Forms of Ellipsis and Evidence for Recovering the Omitted

• Qaṣr conveys abundant meaning without omission; ḥadhf relies on a recoverable omission
• Qaṣr applies only to scripture, ḥadhf only to poetry
• Both must omit a subject
• Ḥadhf requires no contextual evidence