That includes the manufacture of almost $1 million worth of P on March 7, 2010, conspiring to supply substantial amounts of precursor substances and equipment, money laundering and attempting to pervert the course of justice.
Duncan's jail sentence includes a concurrent sentence for conspiring with Tauranga associate Kennedy O'Connor Williams, 26, to recover a bucket containing $500,000 buried in Duncan's Omanawa property while it was under police guard after it was raided in September 2010.
As a result of his drug offending, Duncan has also had to forfeit $2.4 million worth of assets to the Crown, including a lifestyle block, 50ft launch, and a fleet of cars under the Criminal Proceeds (Recovery) Act.
Former policeman and real estate agent, Nigel Walker, 47, was sentenced to 12 months' home detention and 200 hours' community work after he was found guilty at his trial in November of one count of conspiring with Duncan to money launder some of his P-dealing proceeds.
The later charge relates to Walker's offer of assistance to Duncan in relation to his $400,000 planned purchase of an industrial unit in Mount Maunganui's Aerodrome Rd in September 2010.
Tauranga mother-of-five Stacey Helen Clark aka Russell, 36, was sentenced to nine months' home detention and 80 hours' community work after she was also found guilty of one count each of possession of 2.8kg of cannabis for supply and supplying electronic scales to Duncan.
The Crown sought at least half their sentences for the four jailed men but Justice Woodhouse said he agreed with the men's lawyers that their ultimate release was best left in the hands of the Parole Board.
Justice Woodhouse said despite the gravity of their offending, he was satisfied that minimum non-parole periods were not warranted after taking into account the prisoners' personal circumstances, expression of remorse, guilty pleas, and the rehabilitative steps taken.
The judge also noted that none of the offenders had previous drug manufacture or dealing convictions.
After the sentencing, Bay of Plenty District police crime manager, Detective Inspector Tim Anderson, said the six-month police operation that led to the arrests resulted in 16 raids on properties in the region.