The man who gave the gun to the teenager who killed police accountant Curtis Cheng has been warned his sentence could be affected because he has refused to stand in court.

Raban Alou, 20, pleaded guilty to aiding, abetting, counselling and procuring the commission of a terrorist act, by giving a handgun to 15-year-old Fahad Mohammed at the Parramatta Mosque in October 2015.

Mohammed then used it to shoot Mr Cheng outside the Parramatta Police Headquarters before being shot dead by three special constables.

At a sentencing hearing in Parramatta on Monday, Alou's barrister Matthew Johnston SC said his client did not want to stand for religious reasons.

Justice Peter Johnson then read from a document written by the Australian National Imams Council, which he said contradicted Alou's reasoning.

"There is no religious basis to prohibit either standing up for courts or bowing to judicial officers," Justice Johnson said.

"Those matters are entirely consistent with religious beliefs … and the application of Muslim faith in courts in Australia."

Curtis Cheng's (L) wife Selina (second from left) will provide an victim impact statement to the court. ( Supplied: NSW Police )

Justice Johnson gave Alou time to reconsider, but Mr Johnston said his client would not change his position.

"I took the stance of bringing the Imam publication to the attention to the parties so there could be no misunderstanding," Justice Johnson added.

"There may be ramifications for [Alou]."

Crown prosecutor Paul McGuire SC told the hearing Alou should receive a hefty sentence because of his extremist views, his lack of contrition and remorse, and his poor prospects of rehabilitation.

He told the court that Alou made a phone call to his mother from prison last year saying he did not regret his actions and was never going to say sorry for what he did.

Mr Cheng's family has been watching the hearing unfold from the front row of the public gallery.

The court will hear a victim impact statement from Mr Cheng's wife, Selina Cheng, later in proceedings.