With my mini-sumo Seeker 2, it hunts for the opponent. It never assumes its blindly pointing directly at the object once it sees it. It homes on the object even while the object moves around. It does this by constantly checking if the object is in view with both IR sensors, and turning towards the one that does see it if only one does.
That's harder to do with just one sensor, but you just need to constantly update where you think the other object is relative to your robot as you turn towards it.
Track it in real-time, in other words. Don't take a reading, and then blindly turn to the direction you think it was. Think about how you would navigate to a tree in the middle of a park. You don't take a bearing on it, close your eyes, and then turn in the direction your head was pointing, and then walk the right number of steps to get to the tree. You'd never hit it dead on.