Perhaps I focused on the wrong facets of your question.
Regarding boundaries, it's easy to think of examples that are a little less cut and dried. For instance. What is the boundary of the Earth? It's tempting to think of the Earth's surface, but there is also the atmosphere. And, as you know, the atmosphere grows less dense with altitude. You can't draw a boundary, except arbitrarily.
Maybe another option is the idea of atoms as a solar system. Where does the solar system end? The Kuiper belt? The Oort cloud? And then when? You could imagine the heliopause, but that is arbitrary too.
If you look at solar systems from the point of view of the galaxy, each solar system can be imagined as a point, yet as one gets closer, each of them gain fuzzier boundaries.
On the scale of the universe, each galaxy can be thought of as a point...or at least a ball. In this image, each little dot is a galaxy (and big dots are clusters of galaxies). Yet we know of each galaxy as an object with an ill defined boundary. And even at these large scales, we see filaments, nexuses and voids.
In short, the idea of little hard objects with boundaries is really wrong all levels of the universe. Even the smoothest mirror has surface imperfections that are small.
Maybe this helps?
Note here that I avoided all of the wave thing. That's an entirely different kettle of fish.https://wwwmpa.mpa-garching.mpg.de/galf ... _D_063.jpg