I think you're over complicating it in your head and that's making it difficult for you to see. You need a different perspective. Instead the perspective you need is that you rate each of the candidates and then put that into the system. The system will look at all the ratings and determine which has the highest agreeability as a whole. If you're too focused on your own individual "should" then maybe this is hard. You'll over think how you should play the strategy and game the system to make your preference dominate. But the entire point of cardinal systems is to take this out because we don't want people gaming the system. We just want to find people's preferences and elect candidates that are most representative of the people.

You're having a hard time figuring out "the effect of your vote" because the entire point is for you to not be able to game the system. Obviously no system is immune to strategies and there very much are some here. But they don't have huge effects on the whole election. I mean we don't want to violate the monotonicity criteria.