The other was that the seeker had a limited field of view (FOV), which meant it was possible for the target to escape the seeker by flying at right angles to the missile, maximizing its angular velocity relative to the seeker.
The other was that the seeker had a limited field of view (FOV), meaning it could only see the target if it was in front of the missile. This meant it was possible for the target to escape by flying at right angles to the missile, maximizing its angular velocity relative to the seeker.