Hang on a minute. I'm pretty sure that a binding agreement can't be implemented if it allows a parent to pay less. Look you're being a bit vague. I'm wondering is your concerned that because he earns more you get less family tax benefit?
I fail to see how his income impacts your Centrelink payments. Even if your family tax benefit goes down, your child support would go up to rectify the situation
The agreement was done 3 years ago. His earnings in the last few months have almost quadrupled. So that now affects my Centrelink payment.