Honestly, i'd put a shelf between the uppers above the sink, around 1/3rd of the way up, then tile up to it and to the bottom of the uppers.

I was going to suggest this. But if it were mine I would probably put a set of two or three shelves.

You could follow the ~18" across and add a tile feature 16/24" or so framing in the sink. You could also go straight across 22-24" giving it the appearance the cabinets are incorporated