The fact is that not all RPs do use maintenance as it's supposed to be used i.e. for the children. Most do. Some don't. Some are just crap with money. My DSD's Mum is constantly in debt (and no, it isn't because my DH has EVER shirked maintenance payments, walked out on her or anything of the sort, she just overspends and has another child whose father doesn't pay any maintenance).
There's an amount that must be paid by law. If a NRP has a good relationship with the RP, trusts him/ her and doesn't see a lot of the kids or play much of a part in their day to day life, then absolutely, if they can afford it they should pay what they can over the required minimum. We have a friend whose ex puts everything she doesn't spend on their DS from our friends' maintenance money into a child savings account for the DS. She's even sends our friend quarterly bank statements from the account so he can see what's gone in. Everyone's happy.
There are circumstances when it doesn't make sense though. My DH now pays what's required of him after years of paying more. He also pays directly for my DSD's uniform, hobbies, school trips, birthday parties, haircuts and whatever else. If that money went to Mum, it would get swallowed up by debt repayments and other household spending, quite possibly on a child that has nothing to do with my DH. DSD would go without birthday parties, hobbies, new school shoes etc. I'm not slagging Mum off. It is what it is.
No Mum's not happy. But DSD isn't going without either. And DH does see a lot of her and is very much involved in her day to day existence so he'd know if she was.
I don't think you can attack anyone for not paying over and above what's required of them. It doesn't always make sense to give the RP more than one is obliged to.
I assumed from your first post that the difference was fairly significant OP, in which case from my DH's experience, if you have qualms about maintenance being spent on the children, I'd pay what's required and have your DH spend whatever he can afford over and above that on the children himself. Maybe he could agree to buy all their uniform, pay for violin lessons, swimming...whatever.
If the amount is nominal though, and leaving everything as it is will prevent all hell breaking loose then you'd probably be better off leaving it as it is. On the plus side, she's more likely to discuss it with your DP than the CSA next time she has concerns.
And no, the CSA aren't the police. But they are bloody incompetent and I think it's very understandable that NRP's are nervous about being accused of paying less than they should.