The defensive position proves to be well conceived. Perhaps the presence of the narrow pass leads to locations for growing food that thwart the prospects of siege. In any case, to this point, the defensive strategy is effective, and where the Lamanites in the previous war had blitzed through the Nephite countryside, in this war the Nephites were giving good account of themselves. It may be that they were in a more defensible position in this case.
The dead of the Lamanites are cast into the river, which leads to the sea. We have seen this behavior previously for the Nephites. See the commentary following Alma 3:3.