This is an interesting distinction, and were it not for the "passage or safe passage" phrasing in Rule 8, I'd almost have considered it a drafting oversight.

Farwell's considers both situations to result in a "dual action" requirement where both are close to give-way; the sailboat is still required not to impede, and needs to keep that in mind when taking action, but similarly the ship is still obligated to take the appropriate action herself.

An older US case (Linehan v. United States Lines, Inc., 417 F. Supp. 678, 692 & n. 29 (D. Del. 1976)), using the previous Rules, had this statement relating to the narrow channel rule (emphasis added):

This Court, however, is not convinced that the meaning of Art. 20, as amended, is to make the sailing vessel the burdened vessel. The legislative history is not clear, and the one case discussing the change recites the rule in dicta in circumstances where the sailing vessel was clearly at fault. A careful reading of the legislative history and the wording of the statute indicates that the intent of Congress was not to change the status of the sailing vessel as privileged, but rather to limit her right as privileged vessel to set a course which endangered other shipping in narrow channels. The change is no more than a codification of the requirements of common sense and prudential seamanship previously enforced by the courts. No vessel, even before this change, had the right to insist on her status as a privileged vessel to the detriment of other shipping. Particularly is this so where the relationship is that of the heavily laden freighter in a narrow channel meeting the more maneuverable and shallow-drafted sailcraft. This Court, therefore, interprets Art. 20 as (1) placing the burden of avoidance upon the steam vessel, provided she may continue within the channel; and (2) limiting the sailing vessel to those courses which will not restrict the ability of the freighter to stay within the channel.