As promised I would try to explain why I think that the three outside boats don’t have rule 18 rights or obligations between them in this post: Seven at the Leeward Mark, LTW Readers Q&A (60)
To do this I’ve created a much simpler situation involving three boats:
We have Grey, Purple and Red all sailing toward a leeward mark to be left to port. In position one Red enters the zone. Rule 18 switches on.
Both Grey and Purple have to give Red mark-room because she entered the zone clear ahead (RRS 18.2(b), second sentence.)
However, between Grey and Purple, rule 18 is not yet applicable. Provided she does so with rule 16.1 limitation and has no rule 17 limitation, Purple could luff and keep Grey outside the zone. She does not have to give mark-room to Grey, although rule 18 is switched on between her and Red.
Now we come to position two.
Both Grey and Purple still have to give mark-room to Red. In position 2 Purple enters the zone so now rule 18 is applicable between her and Grey. Grey has an inside overlap and is entitled to mark-room (RRS 18.2(b), first sentence)
This simplified scenario indicates that although all three boats are subject to rule 18 once Red enters the zone, that rule does not apply between the two outside boats as long as they themselves are not in the zone.
If I apply that principle to our Seven Boat problem:
In position two we have four boats inside the zone and three outside. Red, Purple and Blue all have to give mark-room to the inside ‘four’. But because none of those three have reached the zone themselves, RRS 18 does not apply between them. Red must keep clear of Purple, who must keep clear of Blue, all under RRS 11.
I hope I’ve clarified my view, and now await your punishment.