1-circle means that the 2nd plane turns towards the 1st one because the 2nd plane counts on it's tighter turn, smaller turn radius to bring it in a favorable position already before they both complete a half turn (180 deg).
2-circle means that the 2nd plane turns away from the first one, because it considers to have a wider turn but a better turn rate (makes a 360 deg turn in less time) and that will bring it in a favorable position after 1 full turn (360 deg).