Threads like this always make me laugh, when people start frothing about how NRPs should give up all/most of their income.
The reality is if you're a NRP you have to house, clothe and feed yourself, and your DC when they visit. So that means living in a home with enough bedrooms so your DC can stay over. If the NRP has a reasonable income, CSA minimum of ??200-300 should be perfectly adequate, and leave the NRP with enough to live on as well. The only families I know who are really struggling are the ones where the NRP pays nothing, and is utterly uninvolved (so the DC suffer financially and emotionally).
My own bf is NRP, he pays what the CSA have assessed. Could he afford to pay more? Yes, if he lived in a bedsit. But would that be in his DC interest? He has them overnight twice a week, so they need their own rooms to sleep in. Or he could just feed them beans on toast. Or never take them anywhere.
But what message does that send DC? Most children have no idea how much the NRP pays for them, nor would it matter to them. However would it matter if every time they visited the NRP they just got horrible cheap food, or never got to go anywhere, or had to sleep on a Zbed? Probably - especially if life with their NRP was decent food, nice home, and trips out, all partly funded by the NRP's additional contributions! How does that benefit those children? It just looks like the NRP isn't that interested in giving them nice things...
My bf has a relatively small net disposable income after he's paid CSA, and for his home. His Ex has a pt job, tax credits, her CSA money, child benefit, a mortgage which is roughly 1/4 what bf pays in rent, and a much bigger disposable income (about 4x his). I can't see any justification in that situation for him to pay more, especially as doing so would actually be detrimental to the DC in the time they spend with him.
I do feel all NRPs should be compelled to pay something. But I don't consider paying more than CSA minimum is appropriate in many cases.