How to blur the "Distance To Nearest Surface" mask in a certain direction?

Development Rendering
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How to blur the “Distance To Nearest Surface” mask in a certain direction?

Imagine that this is a small island on a place where the wind flow zone is indicated in white, a place where there will be no waves.

To do this, I decided to use “Distance To Nearest Surface” as a mask, then shifted and blurred using “Smoothstep”. Obviously, this is not the best solution, on small objects it is noticeable that the texture is shifted.
Tell me how to blur the mask in a given direction?
Maybe this can be done using “Custom Material Expressions” but I couldn’t figure out HLSL

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Generally blurs are achieved by taking multiple samples from different positions and then compositing them together. So you have the right idea of offsetting the sample point. But to properly blur you need to repeat the sample several times from different spots. Usually the more samples, the smoother the blur, but the more expensive.