The location fore and aft where the mast is stepped is controlled by the Class rules.

With the mast spar perpendicular to the base line, the after side at deck level shall not be less than 3048mm and not more than 3202mm forward of Station 11 (the transom)“.

Some people step their masts as far aft or close to as far aft as possible. HOWEVER. You generally do not want the aft end of the mast to touch the back of the deck level gate when you rake. If it does so too early in the rake range, the mast will bend around the back of the gate. When the mast bends down low at deck level it tends to become straighter further up the mast which can make your mainsail too full and powerful up high which you don’t want in overpowered conditions.

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Why the mast should not bend at the mast gate when over powered. (work in progress)