A judge has acknowledged the family of aspiring pastry chef Miming Listiyani might find her killer's prison sentence "completely inadequate" given the extent of their loss.
But Acting Justice Jane Mathews on Wednesday said she hoped they understood sentencing was complex as she jailed Khanh Thanh Ly for at least 13 years over the violent 2016 murder.
"You have lost a beautiful, much-loved and highly-valued person who was central to your lives," the judge told the Listiyani family before handing Ly a maximum 18-year sentence.
"You will no doubt think the sentence I am about to impose is completely inadequate, given the extent of your loss.
"I hope that you will understand that sentencing is a complex process and there are many factors to be taken into account."
The maximum sentence for murder in NSW is life imprisonment and the standard non-parole period is 20 years.
Ly pleaded guilty to the murder after he was found standing over Ms Listiyani's naked body in the shallows of the Parramatta River in April 2016.
They had met earlier in the night to exchange some personal belongings after ending a two-year relationship.
The judge said Ly, now 37, attacked his 27-year-old ex-girlfriend after they left a Sydney hotel. A number of residents nearby heard a woman's screams.
Ms Listiyani's injuries were consistent with her head being banged into the pavement multiple times and there were signs of attempted strangulation.
"It is difficult to imagine the agony and trauma experienced by the deceased in those last minutes of her life ... she did nothing at all to provoke the violence," the judge said.
After fatally injuring Ms Listiyani, Ly put her body in the boot and drove to Cabarita Park, where he was seen dragging her towards the Parramatta River.
When police arrived he was standing naked in the water over her undressed body.
A sentence hearing previously heard Ly has fragmented and incoherent memories of the night and can't explain what occurred.
Justice Mathews on Wednesday said she was "thoroughly convinced" he wouldn't have murdered Ms Listiyani were it not for his then untreated post-traumatic stress disorder.
She said she had rarely seen an offender as "remorseful and devastated by his own actions".
Experts say Ly has excellent prospects of rehabilitation if he avoids alcohol and illegal drugs and receives appropriate mental health treatment, the judge said.
He will be eligible for parole in April 2029.
Ms Listiyani's family did not speak to media as they left the hearing but her father, Sem Eu, has previously told the court he never dreamed his family would experience such a tragedy.