My reading is that at a gate the least important rule is the overlap. Rule 18.1 says (emphasis added) "Rule 18 applies between boats when they are required to leave a mark on the same side and at least one of them is in the zone."

At a gate, the two boats are not required to round the same mark. So the overlap is not in any way relevant. As far as I can see port-starboard is the only rule in effect. Am I right?