Wirihana was among the 13 people arrested in the initial investigation.
In the Court of Appeal in Wellington today, Wirihana's lawyer, Russell Fairbrother QC, said his client's involvement in the drug ring was low-level.
He said Wirihana was a "small time user", who used meth to get through long working days while he worked two jobs.
Fairbrother argued Wirihana's sentence should be adjusted due to a change in the standard the courts used to judge similar offences.
The justice system had recently adopted a new standard for this type of offending - different to the previous standard Wirihana had been sentenced in line with - and his sentence should now be "scaled back accordingly", he said.
But Crown lawyer Meetra Wong said the starting point the sentencing judge adopted was already "extremely generous".
She said a starting point of at least six years in prison would have been available to the sentencing judge, who instead adopted a starting point of five years.
The Court of Appeal has reserved its decision.