The fuse detects targets to the side of the missile, not directly ahead - the sensitive area is essentially between two (conical) surfaces near to and slightly ahead of the missile beam area.

With sloppy guidance this allows the whole fuse sensitivity to be used on a regular basis (once the missile is at the correct relative range from the launcher, the lateral offset may approach the fuse sensitivity limit), with tighter guidance of at short ranges the correct relative range will occur with either a direct hit or a very close miss.