I think you’re looking into the example a bit too far. I made that example to show the issue I’m talking about in its simplest form. My actual use case is far more nontrivial but is being hampered by the artifacts caused by fmod and frac – basically anything that causes a hard seam of uvs between two nearby fragments will cause it to do a weird interpolation artifact on the boundary between them.
You are right, though. If I needed to do what is in the example, I would just tile it as you described. The question itself is to avoid the artifacts from fmod and frac