Mr Kumar's family did not provide victim impact statements to be read in court and said through prosector Kieran Raftery that they felt there were no words that could explain their tragedy.
Earlier this week the family said they would not attend the sentencing in a boycott against the justice system they said failed them.
They were particularly distressed by the defence counsel's position that the 14-year-old had been acting in defence of Mr Kumar, who had armed himself with a pole after the two teens entered the dairy.
In sentencing, Justice Lang said he was not satisfied by the defence's claim the teen was acting in self defence.
Mr Kumar was acting "completely defensively", he said, and was "in a vulnerable situation" when confronted by the 14-year-old with a knife.
The teenager's early-life and upbringing that was "turbulent in the extreme" was the underlying factor to his actions in the Railside Dairy, Justice Lang said.
The 14-year-old suffered a "serious traumatic brain injury" when he was struck by a vehicle at age 8.
His mother drank alcohol heavily and took drugs during her pregnancy, Justice Lang said, and the 14-year-old had symptoms of Foetal Alcohol Syndrome.
He was addicted to synthetic cannabis at the time of the attack on Mr Kumar, and was living in a house that was used by drug-takers.
Justice Lang said an expert had told the court the teenager's brain injury made him "extremely vulnerable to complex factual situations".
The teenager's lawyer Maria Pecotic said Justice Lang should not compare his case to that of Bailey Kurariki, who was sentenced to seven years imprisonment for the manslaughter of pizza delivery worker Michael Choy because of the elements of pre-meditation and the number of other offenders involved.
Justice Lang agreed. He said there was little assistance the case could give to his sentencing today.
He put his starting point for sentencing at seven and a half years in prison. He took into account the teen's youth, he said, but would only place light weight on the teenager's brain injury, saying that discount had already been given by the jury.
"I have no doubt you would have been convicted of murder [otherwise]," he said.
He settled on a sentence of six years imprisonment with a minimum non-parole period of three years and three months.
The Crown were seeking a starting point of 10 years imprisonment for the teenager.
Justice Lang said the family of Mr Kumar were "forced to relive their family member's final moments" throughout the trial.
"They will never be able to replace Mr Kumar. They will never be able to live their lives as they were [before his death]."
