Windward mark: Both must tack

Is the diagram at the foot right?

Starting point P on Port, S on Stbd, boats on opposite tacks with courses intersecting between one and two boatlengths downwind of the mark.  P reaches the zone first.

@1 when P reaches the zone, rule 18 does not apply (rule 18.1(a)).  Both needing to tack is irrelevant.  Boats are NOT overlapped because boats are on opposite tacks and rule 18 does not apply (Definition:  Overlap).

@2 minus Delta, when P, tacking, passes head to wind, Boats are now on the same tack.  Rule 18 applies.  NOT rule 18.2(b) because boats were neither clear ahead nor clear astern, nor overlapped when P reached the zone.  NOT rule 18.3 because S was not fetching, so only rule 18.2(a):  while they are overlapped, whichever boat is outside boat, at any future instant shall give the inside boat mark-room.  BUT it may be that, initially S is not 'inside' between P and the mark, so rule 18 is turned on, but it has no 'content':  neither boat gets a right to mark-room.

@2+Delta, both boats on Stbd, and S, to windward of P, gets between P and the mark, S is now 'inside' P and P must give S mark-room.  With P starting at the edge of the zone @1, by now S is well inside the zone, and is in all likelihood 'at' the mark, so P must give S room to sail her proper course to round the mark.  S is overlapped to windward and on the inside of P so the mark-room P is required to give includes room for S to tack.

@3 minus Delta, S tacking from Stbd onto Port, passes head to wind, boats are now on opposite tacks, still on a beat to windward, so rule 18 goes OFF, P, now on Stbd tack is RoW boat, but, boats are on diverging courses, so this is immaterial.

@3+Delta, P tacking onto Port, passes head to wind, boats now on same tack, rule 18 comes ON, specifically rule 18.2(a), and if P becomes overlapped inside S, then S must give P mark-room, by now, certainly being room to sail her proper course at the mark.