Impact of relative ball size?

Both ball size and sand depth are aesthetic choices more than functional ones. While Sisyphus readily scales - the largest to date being 3m in diameter - sand doesn't. Although you can get finer or coarser sands, there is a lower limit of particle size (~100 microns), at which the particles start to stick to one another due to van der Waals forces. This is why powders don't behave exactly like sands do. I have used pure baking soda - it works, and produces great detail - but just doesn't look as nice (IMO). This particle size boundary limits smooth rolling of smaller balls (ball:particle size ratio is too low - the ball gets "stuck" and deflected by the particles). Again, it's not a functional limitation - I have used ~1/8" diam. BB's, and they "work" just fine - but they move jerkily. If your goal is to to a picture of a completed track that displays representational content (like text, logos, pictures), then how the ball moves along the path doesn't matter, and using a tiny ball can be an advantage (like using an extra fine point Sharpie instead of a big fat one). But if you are more interested in the "process," then smoother ball transit is a big plus. And when it comes to algorithmic tracks, where the track "stacks" repeated passes of the ball close to one another, incredibly fine detail can result - independent of ball size.

Sand depth is also a subjective call. Sisyphus will "work" over a wide range off sand depths (from zero to covering the ball if you use a strong enough magnet). I prefer depth in the range or ~1/4-1/3 the height of the ball. Shallower sand yields better detail, but deeper allows more intense dune shadowing. Again - it's a purely aesthetic choice.

I encourage you to experiment. You can't harm anything if you use common sense - "sand" can be any particulate that isn't ferromagnetic (though I would avoid foodstuffs like grains / flour). And the ball can be any size that will fit under the LED shade ring. You can get single steel bearings of various sizes at Home Depot (in the specialty fasteners section). And the "ball" need not be a sphere - any ferromagnetic object will work (stay away from sharps though). However, only spheres roll smoothly (in any direction), and rolling is so much nicer than being dragged :).

Thanks for the prompt and thoughtful reply, Bruce!  I'm really looking forward to receiving my coffee table.  My question about "stroke" was more about whether for example a track designed to move the ball down, move left, go up, move left, come back down, and so on might leave a nice column of dunes when played on a "finer point" coffee table, while the Mini's (relatively) larger ball might cause that same track to result in no dunes (or only dunes on either side of the entire path) because the track wasn't designed to move the ball over far enough between "dune columns" to preserve them when a relatively larger ball was used.  But of course right now I haven't even received mine yet, so I'm just thinking about all these things while geeking out on Sandify and other track creation tools, so I may well be thinking of this completely incorrectly.

Most tracks will work with any of those "% of sand field" ratios. However, some tracks might be more sensitive to it, such as my "ying yang" and "it's your move" tracks. They were designed on my 2' side table, which fortunately is in the middle of the ranges. I need to try them on my mini, and I'm curious what they look like on the coffee tables. I'd be happy to create custom versions for different size tables and ball sizes, but without a way to test them, it's hard.