Here's a diagram where the leeward boat does not "close the door" on the windward boat.



In this scenario, Blue does not act to "close the door" on Yellow. She holds her course and Yellow takes advantage of the room given. Neither boat breaks a rule. Blue should lose this protest.

And, here's a drawing that shows the leeward boat "closing the door" too late.



When Blue changes course, she does not give Yellow room to keep clear. Blue breaks RRS 16.1. Yellow breaks RRS 31 (Touching a Mark) but is exonerated under RRS 64.1(a). Yellow should win this protest.

I hope that helps,
Eric