Mr Hart said the offence took place in the middle of the day, the officer wasn't "vulnerable", the vehicle wasn't moving at a significant speed at the time of the impact, and that there was no evidence that anyone else was put in harm's way.
Crown solicitor Mike Smith submitted the starting point was appropriate as Judge Ronayne took into account the totality of the offending and, in particular, linked the offences to numerous aggravating factors of the offending.
Although the officer escaped injury, Mr Smith said the potential for more serious injury was real and considerable.
Justice Simon Moore - who heard the appeal - said although the offending was undoubtedly serious, a global starting point of three years was beyond the range available to the sentencing judge. The lead charge shouldn't have attracted a starting point of more than 18 months in jail, he ruled.
Justice Moore didn't accept that Mr Cumming was vulnerable in a manner that aggravated the offence. "The officer was vulnerable in the sense that he was alone and the weapon was a car but those factors are, in my view, inherent in the charge."