What's the exact criterion of dual submission?
It is up to the editor/conference committee/reviewers to decide if two papers have too much overlap.  Show them about both versions of the paper, and let them decide.

Since there is no objective way to decide if two papers are adequately different, the criterion is the opinion of the editor.

If the editor is unaware of the situation, then you are at risk of committing misconduct.  If the editor knows and approves, you are likely to be behaving appropriately.