Don't think for a minute that any Child Support enforcement agency will work to reduce child support. They claim to look at your earning potential based on previous work history. Doesnt matter if you lose your job, they still want you to pay somehow. They're kind of like credit card companies in that they want to keep you in the system as long as they can. If you don't pay, the fees will continue to add up and you will never escape it.
As far as the other parent's income; it depends on the state law. In the Fkd-up Texas System, they only look at the non-custodial parent's income. Tramps like the one I was married too can sit on thier ass' and collect child support or welfare.
It's like this; your money is their money and their money is their money!