Thanks - I have let it go but made sure he has acknowledged in writing the period for which he will be obliged to pay CM and the GOV.UK calculated amount based on his salary and nights he has the children to stay.
He does keep saying that when settlement is final he will have them more often..I suspect to reduce his liability and I don't think there's anything I can do about that if they are willing to go and stay with him.
Child contact must be for the benefit of the children, not just used to reduce CM liability. Bear in mind the CM rate is the statutory minimum. It is perfectly open to him to pay more to ensure the children are OK. You can only enforce the minimum though.