C can start buffering early because they know where B will turn. It should be easy to stop the cut in the first few iterations.
Remind C to continue defending all the way until B reaches the cone.
If your group is skilled at this, you can eventually remove the top cone. The cutter can cut under at any point on that straight line to the opposite middle cone. This will require more anticipation and provides more game realism for the defender.
Running this drill on both sides is great for helping participants practice turning to different sides and getting defenders looking over different shoulders.