The zone snapshot

Facts found

Both boats run down to the leeward mark on starboard gybe. A is clear ahead when she reaches the zone. Well inside the zone B pulls up on A's inside, becomes overlapped to leeward, and hails for room. A ignores the hail, sails to the mark and rounds close. B has to luff hard and swings wide. B protests.

You are on the protest committee.

How would you decide this?

Decide it cell by cell instead