So my perspective I get £200 from ex for my Dd which is supposed to account for half her nursery fees but it doesn't but it's a nod. Big ticket items I tend to pay for because I'm a much higher earner and buy all clothes, essentials ect. I suspect we will go half's on uniform but I won't be fussed if we don't as I refuse to bankrupt him and for me it's a privileged position I find myself in financially.
DH pays his ex £200 per month for DSD 11 and goes half on uniform, shoes/trainers/clothes. He also has a tendency to pay for things out right such as laptop, iPhones and games when the ex/DSC asks because the ex works part time so money is tight their side. She's rather furious she has to work at all tbh but those are the breaks unfortunately with the current benefits system.
It's so situational, I can do what I do due to my current situation which could change, same with DH.
CMS calculations can be flexed to suit the narrative of the person inputting the info, rarely does cover actual cost of raising a child.
Big ticket items go half's, uniform can break most peoples accounts or make a large dent (secondary school especially), non essential stuff is up for debate. No kid needs 5 pairs of Nike trainers. If you want your kid to have 5, then you need to pay for that privilege and can't expect someone to have the same value on 5 pairs than you would.
I will say though as a SM I found it incredibly cheeky that DM was hoping my salary would be taken into account when hoping to up financial maintenance for DSC. That was CF move that nearly meant DSC got less (from me personally as I buy her riding boots, games tech just because I can) because of the sheer tomfoolery about it. Sad thing is as a mum, I'm happy to help out another mum, esp SDM but that was a step wayyyy to far for me.