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The legal wording is always confusing I am afraid.
Your ex no longer has any personal claim on your pension or indeed anything else.
However this is about maintenance for the benefit of the child - not your ex - and I am afraid that yes the CMS can indeed take your Pension Income into account.
Indeed even if you have a greed a figure for Child Maintenance in the Order then after 12 months the CMS assessment would override it
Please ask if you need further details