If there was no overlap at the zone, then the boats clear astern would have to give room no matter if an overlap later became established. The boats on port would also have to keep clear in accordance with their obligations under rule 10, but that is secondary in the incident being discussed.

As far as protesting, you would protest the boat to windward which you consider to be taking room they are not entitled to.

If I were the protest committee hearing the incident, I would likely dismiss the original protest and open a jury initiated protest with all boats involved as parties, allowing all testimony to be heard and hopefully figuring out what actually happened.

Without knowing how the overlap was established, making a judgement is very difficult.