Child Maintenance Struggles

[YellowBanana]

I have a 13 year old daughter with my ex husband. We divorced when she was 3 and he paid child maintenance calculated through the CSA. When his disbanded he continued paying the same amount and never disclosed any increase in income. This year I asked for a review through the CMS. My ex now has two other biological children, a step daughter and two foster children. I believe he gets in the region of £50k tax free per year for the fostering which is paid to his partner. CMS have reviewed the calculation and have increased his payment amount. He is contesting this on the basis that the fostered children should count as children in his household and therefore should be included in the child maintenance calculation formula. However he is also using only his salary, not the amount paid for the foster children by the state as his income. He has recently told my daughter he is planning to move jobs to become a teacher - I believe he can only do this as he has such significant income from the fostering. He will no doubt argue that the child maintenance for my daughter moving forward should be based only on his new income. Can I make an argument that the fostering payments are facilitating this change in employment and therefore should also be considered as his income? They have a large house, multiple cars, motorbikes, football season club memberships etc.