Question
Under what circumstances can A establish a leeward overlap from clear astern
and still have the right to sail above her proper course?

Answer
Figure 1: The overlap is established when the boats are more than two lengths apart. Rule 17.1 doesn’t apply to A and she is entitled to sail above her proper course.

Figure 2: The overlap is established when the boats are less than two lengths apart. A may not sail above her proper course while the boats remain within this distance. However if A sails more than two lengths away from X without breaking the overlap, she no longer has a proper course restriction and is entitled to sail above her proper course.