Anderson appealed his sentence on the basis that given the principal of parity, the starting point of nine years was too high.
His lawyer Nick Leader argued in the Court of Appeal that Cameron's level of culpability in the robbery was higher, yet the High Court adopted a starting point of seven years.
Leader said the discrepancy in both starting points was so stark, unjustified and irreconcilable that the appeal should be allowed.
The Crown submitted the High Court judge adopted a more lenient starting point for Cameron because he was being sentenced for a second strike offence and was therefore required to fully serve his whole sentence without parole.
The Court of Appeal said it must allow the appeal if it was satisfied there was such an error that a different sentence should be imposed.
Ultimately, the court said the focus was on the sentence imposed rather than the process by which it was reached.
"In this case, having reviewed the two sentencing decisions, we are of the view that there is a gross and irreconcilable discrepancy between the respective starting points," the court judges ruled.
In contrast to the role Cameron played, the judges said Anderson was a secondary party whose principal task was to support the other offender and to maintain guard over the victims.
They were satisfied Anderson was sincere in his expressions of remorse and expressed a willingness to engage in restorative — an offer three victims appeared to have taken up.
Anderson's sentence was substituted with a term of four years and seven months.