statutory payments

Can anyone help with a moral dilemma
My stbx and I had a family based(F.B.) arrangement where we agreed that I pay a fixed amount of money to her for our 2 children + additional payments when needed for things such as school trips new school uniform, costumes for dance and drama performances, uniform for pony club etc etc. I found that this was a satisfactory arrangement even though I sometimes found myself financially stretched with the additional payments

after an argument my stbx felt she could get more money from me by applying for a CSA statutory payments
The CSA assessed my salary and came up with a figure that I am obliged ( and happy I must add) to pay. The amount is about 10% more than the fixed amount I was paying on the FB arrangement
the question is, now that My stbx decided that she wanted a Statutory arrangement I feel I''m legally and morally obliged to pay just what the CSA state I pay. My stbx is still looking for me to make additional payments but my view is that the Statutory payments now cover all payments.
can anyone give me a definitive answer as to what child maintenance payments pay for
and should I continue to make additional payments. I should add that when the children are with me I do buy them clothes when they need them

Child maintenance through the CSA covers all financial requirements for your children. You are under no obligation to pay above and beyond what the CSA dictate you should pay. Your ex has not only cut her nose off to spite her face by using the CSA, but obviously damaged any amicable relationship you may have had!!

My ex done the same. Was quite happy for me to help towards school uniform, shoes etc until I started divorce proceedings. He then went via csa so I stopped all other financial help. It kills me when my kids say he can''t afford new shoes, parties etc, but at the end of the day it was choice to go csa and he has lost out and uses that as an excuse to the kids