My small tank is 5" x 7" and my paper is 4" x 6" or smaller. Technically, that's not miniature. But it's definitely small. There are so many interesting things you can do in a smaller tank that just aren't possible in a larger one. And when you do do something that is possible in both tanks, the effect is very different. And I like different. In the example above, I pulled a stylus (in this case a straight pin) through stones (more like pebbles). I think that in smaller tanks, you get more bang for your buck with this technique ~ the design is more defined and dramatic.
In my two-day Introduction to Marbling class, students have three different tank sizes to experiment in ~ and the small one is one of them. Since we always start off in the big tank (20" x 25"), it's a bit of a stumbling block for some to switch gears so dramatically. But once they get the hang of it (you really have to pay attention to the amount of paint you are using), they let go and have fun, especially with the stylus.
I rarely name my pieces but this one I did. I call it, "Kelp." When I am snorkeling near a thick kelp bed, this is sort of what you see when you're looking down toward the ocean floor.
And this is what the fish see when they look up:
I think we have the better view!