I'd vote for that guy!
I think it's totally fine. The ex apparently just likes drama. I mean, I get feeling "left out" or slighted because of things like this -- I've been there in regards to my daughter & her father, but I know it's stupid & move on without making a fuss. I mean, really, that's the only reasonable way you could have worded it.
My husband suggested doing a mock-up of one:
"Candidate lives with his wife Proto, their son E who may or may not have been conceived on their wedding night but may have been conceived the week before and it doesn't matter because they were living in sin for three years before that anyway, and HIS daughter from his first marriage, but only 35 percent of the time based on the parenting plan jointly agreed to by Candidate and (EX'S NAME), although in actual practice it comes out to be closer to 37 or 38%, depending on whether EX is doing anything interesting for Christmas."