Why is ījāz al-ḥadhf treated as a separate next section?

Musāwāt and Ījāz al-Qaṣr: Proportionate Wording and the Rhetoric of Qiṣāṣ

• Because it invalidates all cases of qaṣr
• Because it declares musāwāt ineloquent
• Because it deals only with identifying poets
• Because it examines real omission and the clues allowing recovery