Mohammed Waqas managed to lose his supervising officer while with family at a mosque and remained on the run for five months.
He had been jailed for almost nine years in 2019 for a machete and baseball bat attack on a man at a petrol station in Tipton.
The 30-year-old had been moved to Sudbury Open Prison in Derbyshire from HMP Birmingham and was allowed to go to the funeral in Saltley, Birmingham, in January accompanied by only one officer, and not in handcuffs, because he was a "model prisoner".
But Birmingham Crown Court heard the officer was left feeling intimated by the number of people surrounding Waqas at the funeral and so did not pursue him when he walked away.
Mr Andrew Davidson, prosecuting, said: "The officer warned the defendant he would be classed as unlawfully at large if he did not come back with him.
"The officer asked him to come. He did not, then he got up and walked away. The officer felt intimidated by the number of people and did not try to pursue him."
Waqas was eventually caught on the run when officers stopped him in a car, believing he was acting suspiciously.
He was originally locked up over an attack at the Texaco petrol station near Tipton Morrisons in May 2018, where a 31-year-old man was beaten and left with injuries including a stab wound which needed surgery.
The court was told how Waqas had 24 previous convictions but that he had become a "recovery champion" in prison, helping other inmates with drug addiction problems.
It was for this reason he was trusted to leave the open prison with only one officer and out of handcuffs, explained Recorder Paul Bleasdale.
He said he did not accept grief over his mother's death from Covid as an acceptable reason for not handing himself in to police, as he sentenced him to an extra six months behind bars, on top of the sentence he was already serving.
Waqas, of College Road, Birmingham, pleaded guilty to remaining at large after temporary release from prison at an earlier hearing.
Recorder Bleasdale said: "Because of your character you were trusted and allowed to go to the funeral with one officer.
"With complicity, I regret to say, of family or acquaintances, you did not return to the custody of the officer who accompanied you. He clearly faced a difficult position and was intimidated by what was going on."
He added: "You were a model prisoner and have lost the privileges you had with an open prison and I doubt you will regain them."
Mr Haroon Khattak, defending, said it was never Waqas's intention to remain at large.
He said: "He was overcome with emotion. He is an individual who was very close to his mother and was struggling to mourn."