Yeah, the rules obviously contradict themselves. My gut would also be to go with the playbook, if for no other reason then because, that´s the part of the rules most accessible to the players. But I´m sure it won´t break the game if you decide to go with what you like best.
And for the record: I don´t interpret high-powered as a choice: If you add it to a weapon with the close tag, it gets close/far, and if you add it to a weapon with the far tag, it gets +1-harm (making your rifle shoot more powerfully doesn´t add to its ability up close). So functionally equivalent to adding a scope.
Again though: It probably won´t ruin anything if you allow the choice.