Jinās al-qalb ordinarily relates two distinct words whose letter sequences are reversals of one another. Reversible qalb instead requires the chosen utterance to be identical to itself under reversal.
The first compares two expressions; the second compares one sequence with its own reverse. Their shared name must not obscure this different unit of analysis.
Showing that one word is the reverse of another does not prove that a sentence containing both is itself a reversible sentence.
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Qalb, Tashrīʿ and Luzūm Mā Lā Yalzam: Completing the Verbal Ornaments
Jinās al-qalb ordinarily relates two distinct words whose letter sequences are reversals of one another. Reversible qalb instead requires the chosen utterance to be identical to itself under reversal.
The first compares two expressions; the second compares one sequence with its own reverse. Their shared name must not obscure this different unit of analysis.
Showing that one word is the reverse of another does not prove that a sentence containing both is itself a reversible sentence.