فَإِذَا لَمْ تَفِ بِالْغَرَضِ سُمِّيَ إِخْلَالًا
When brevity fails to serve the intended purpose, the result is called ikhlal, a defect in expression.
A poem can be shortened in a way that removes the clue needed to understand its analogy. The problem is not shortness by itself; it is the loss of a recoverable intended meaning.
Sound ijaz: few words, a clear meaning, the purpose fulfilled.
Ikhlal: few words, but an indispensable meaning is missing or insufficiently indicated.
The audience and communicative context decide whether an abbreviated expression is effective.