You place a continuous shim the thickness of the grout lines on the leveled countertop and tile on top of it. Grout the splash, pull the shim, and pump the gap full of 100% silicone color matched to the grout. Spray it with Windex, spit on your finger, and tool it to perfection. Wipe off the Windex overspray before it dries without touching the fresh caulk. That bead will flex with building movement, look good for years, and is replaceable if need be.
The pictured gap between the deck and tile is too small; it may never behave or look right even after the grout is replaced with silicone.
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