finite automata – How to minimize this DFA with already merged states?

The original non-deterministic FSA that I have is:


After converting to a DFA, I get:


When I use the Myhill Nerode theorem for the current DFA, I get all the pairs marked, so this is already minimized. But I think that's wrong.

I want to minimize this DFA. How do I do that with the Myhill Nerode theorem, since some states are already merged?