Lumbertruck: Starting at A18 is 1 point worse on the board, but you end in sente not gote assuming white doesn't want to fight a ko.
caranthir: You are of course right in a way. Then again, we end in sente anyway if we don't answer locally after A17, A18. Usually these endgame problems are only about maximising local profit. We can't assign value to sente if we don't know how rest of the board looks like.
Starting at A18 is 1 point worse on the board, but you end in sente not gote assuming white doesn't want to fight a ko.