Ijaz can work in two principal ways. In ijaz al-qasr, the few words themselves carry a rich meaning; no omitted phrase need be reconstructed.
In ijaz al-hadhf, some word or clause is left unspoken, but linguistic or contextual evidence enables the listener to recover what is meant.
Ijaz al-qasr: richness resides in the expressed wording.
Ijaz al-hadhf: part of the expected expression is absent, with a sufficient clue to its meaning.
A short sentence is not automatically an instance of deletion.