This, in other words, is how my H responds to "boundaries."
He can do that, but a family court judge isn't going to look very kindly on him if his "calculations" are to short-change his own children. Courts are abundantly clear when it comes to child support -- IT'S NOT THE KIDS' FAULT, and parents are to do whatever they need to do to abide by the contribution amounts.
I'll be anxious to hear what your attorney says. I would respond "thank you for your clarity" or some such.