The match racing umpire calls shed some light on this situation, especially UMP5:

CALL UMP 5
Rule 11 On the Same Tack, Overlapped
Rule 16.1 Changing Course
Rule C2.4 While Tacking or Gybing

Question 1
Yellow, a leeward boat, luffs head to wind, and Blue luffs in response, so that both reach positions side by side, head to wind. Blue continues to change course and passes head to wind. In so doing she makes contact with Yellow. There is a
Y-flag. What should the call be?

Answer 1
If, when Yellow begins her luff, Blue immediately responds and continues to do what she is able to do to keep clear throughout the incident but there is contact anyway, then Yellow is not giving Blue room to keep clear and she breaks rule 16.1. Penalize Yellow.

If Blue could have kept clear, but either responded too slowly, not enough, or over rotated, then Blue has broken rule 11 or 13.1. Penalize Blue.

(emphasis is mine)