Courage

"Speaking of Courage" relates to courage in the way that O'Brien speaks about Bowker's interpretation of his courage. In this chapter, Bowker talks about how he almost earned a Silver Star by trying to save Kiowa. However, he fails to actually rescue Kiowa. Bowker deals with the incident by convincing himself that he was as brave as he possibly could be by even trying to save Kiowa.
In this scenario, the courage vs. cowardice line is clearly defined, unlike "On the Rainy River." The courageous choice during the situation would have been try to save Kiowa, and the cowardly choice would have been not trying to save Kiowa at all. However, another line lies in the gray area between the "levels" of courage. Although attempting to save Kiowa was undoubtedly an act of courage, letting go of Kiowa to save himself from sinking deeper is cowardice, which creates the problem of whether the action was courageous, cowardly, or something in between.
Comparing the scenario to "On the Rainy River," where O'Brien seemingly has no courageous choice, "Speaking of Courage" has clearly defined "good" and "bad" choices. In "On the Rainy River," all the choices O'Brien could have possibly made seemed cowardly in nature, but one could argue about how each individual path could also be courageous.
TL:DR - "Speaking of Courage" had courageous and cowardly actions that were easier to see in comparison to the choices that O'Brien had to face in "On the Rainy River."