Csa help pls!! UK

So I went through csa to get maintenance from my ex partner for our three children. It was worked out at band 1 but now my ex has changed days he has the children just so he had to pay less for them. (He does not have the children on these extra days he is at work and gets home when kids are in bed). So now it has changed to band 2. My question is will they work out how much maintenance he pays due to the band  it's in or the actual amount of nights he had the children for? Personally for me it's never been about how much he pays its just that I need to know how much I have coming in each month as I have bills to pay. For him it's all about the money and not children which is so frustrating.