We usually sail Disney, and they have it broken down by who is getting the tip. We always remove the "Head Server", which on Disney is just a random guy who walks up to you once a night and says "How is everything?". He doesn't deserve a tip. But with them, they give you the ability to customize up or down the amounts for each person as you see fit.
My upcoming RCI sailing will only be my second RCI sailing. Am I understanding correctly that tips on your SeaPass are all or nothing? And they aren't allocated, just pooled? I only ask, because often times we find ourselves not going to the MDR, so I wouldn't likely tip that server (unless we actually went). I wouldn't want to reduce my overall total tip amount, but ensure those actually serving me are the ones getting tipped.
If you can't allocate, then it seems the best way is cash tips (which I generally prefer anyway, feel it is more personal)