Inertia, thank you for your personal example! Thats all we were really asking, to make sure DSD is actually benefiting from the CS. If that sounds controlling then i guess we are controlling ... i think DP has a right to ensure his daughter is cared for properly.
I don't find it any more controlling than me controlling what food they eat when I do the weekly shopping, or what clothes they are going to wear when I go buy them. TBBH, the custodial parent some times tends to take these things for granted and doesn't realise that they have all the control in day to day expenses and care decisions. Court custody arrangements used to specifically state that - custodial parent has control over all day to day decisions and any long term are joint. Well I don't agree. DH had just as much right to have a say in what formula I was feeding his bub as I did. Now I know there are some exs out there that would use that kind of approach to hurt their ex. "I dont want him eating $2.50 cheese slices, I want him to be eating $7 ones" - but you know what, thats what child support is for. DH wanted me to stay in the house so he paid half the rent to ensure I could afford to. He wanted his children to be able to have NAN and Huggies, so he put his money towards ensuring that. My XH wanted our kids to have all the advantages of other kids - so his money gets put towards their school activities so they could have the advantages of their peers. Granted he has nothing more to do with them (his decision), but I have made a point of finding a way to cover his wishes for his kids with the laughable amount of money he pays towards their support.

So long as s/he is willing to put in the necessary effort (including money) to be an active part in their childs life, then I am all for them having their say in their childs upbringing. Its not being controlling - its caring for their child.