If you replace the existing caulk with a flexible caulk, that may eliminate the cracking issue.

This is why you place a continuous shim on the countertop that is the thickness of the grout lines, lay tile, grout, pull the shim, and fill the gap with color matched silicone.

You have too small a gap to be filled with enough silicone to expand and contract, therefore it will always be an issue.

What Joe said.

Joe do you have a pic please?

Coved backsplash, but it's the same thing.