Initiative Checks: At the start of a battle, each combatant makes
an initiative check. An initiative check is a Dexterity check. Each
character applies his or her Dexterity modifier to the roll. The DM
finds out what order characters are acting in, counting down from
highest result to lowest, and each character acts in turn. In every
round that follows, the characters act in the same order (unless a
character takes an action that results in his or her initiative
changing; see Special Initiative Actions, page 160).
根据核心P136,决定行动顺序的是先攻检定而非你当前先攻加值,当你投先攻后,你的先攻检定以及攻击顺序就已经恒定下来了,除非角色进行了会导致先攻改变的动作