I'm not quite divorced yet, but I've started doing the same thing. XW will try to bait me - talk about an argument that happened literally 8 years ago. I've started pretty much ignoring everything - I do share things about the kids, and she instantly begins attacking me because she hates it that the kids love me so much - on top of obvious guilt from A.
You are doing the right thing - ignoring the bait, but making sure boundaries are established.
