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It’s not how well you roll that counts but how well the dice suit the game.
Section 8.9.2 states defending forces of more than two blocks must remain outside the castle.
This brings on another question & answer...
If the Ishida force must retreat after the battle then 2 blocks may retreat into the castle and the overage must retreat elsewhere.
This is totally right!
Rule 8.8.4 (final): If a castle is a valid retreat destination, the retreating player may leave up to two blocks in it. If there are more blocks remaining, these must retreat elsewhere as a group.
Your 8.9.2 interpretation is totally correct too. If the defender has more than 2 blocks at the time the enemy attacks, all must go to Battle outside the Castle.