The manual says you can drag Point 4 up and down to set the Level 4 envelope in DX7 Envelope mode. It doesn't work. You can set the Level in the parameter box, but this no longer shows in the Envelope display. This is true in both the Overview and Envelopes tabs.
If you have adjusted Point 4 Level, it is also not releasing the notes if you bring it back down to 0. You have to hit the Panic button to clear them.