Why did the word "عجيب" (amazing/wondrous) appear in its definite form in Surahs Qaf and Hud, while the word "عجاب" (amazing/wondrous) appeared in its indefinite form in Surah Sad?

Part of the eloquence of the Quran is the diversification of its style. Both "al-'ajab" (wonder/amazement) and "al-'ajeeb" (wondrous/amazing) convey an exaggeration in the occurrence of wonder, but "al-'ajab" is more emphatic, indicating that which has exceeded the limit of wonder. Since the disbelievers' astonishment at making the gods one God was greater in their souls than the Warner being one of them, or a child being born to one who had reached old age, it was appropriate to use the term "al-'ajab" in Surat Sad, and "al-'ajeeb" elsewhere.