It is really very simple and you are doing your best to complicate things. There is no need or reason to give any crew member any tips. It is very simple. If you want to, have at it, but there is no need, expectation, or benefit in doing so, and in spite of what others claim you don’t get any better service if you add an additional tip or not.
Don’t over think things.
BTW your OSC and gratuities are so high because your cruise is so long. If you want them to be less, take a shorter cruise.