I'm a bit confused about how the parenting payment decreases when one starts work and was hoping someone *COUGH*BG*COUGH* could help me!

My understand was that if as a single parent pensioner, I earn over the threshold (some 160 odd dollars a fortnight) my entire parenting payment is reduced by 40 cents in the dollar i.e. 40%. My mother says that when she was a single parent working, it was only the amount over the threshold that was reduced. E.G. if I earn $130 for the fortnight instead of $120, I'll lose 40 cents in the dollar for the $10 extra I earned. Is that correct or is it the whole payment? I enquired at centrelink but I didn't understand what the bloke meant! I thought it was my entire payment that was reduced until Mum said otherwise!

Thanks