From a post to ALT.BOOKS.DAVID-WEBER dated September 20, 1998:

Missile orientation during flight

    Missiles in the Harrington universe are virtually all seeking weapons. Their sensor heads are required to maintain lock on their targets (at least once they are beyond effective, real-time telemetry control from the ship which launched them). This means that they keep the throats of their wedges oriented on their targets, which is why it is possible for point defense lasers to kill them at extended ranges. There is no sidewall or wedge protecting them from the fire or the ship they are attacking; their wedges do, however, protect them from the defensive fire of other ships which might attempt to engage them from "above" or "below."