As far as I know, Wille Manson pieces with a flat window to an interior design (like the Bat Cave weight Sue mentioned) always had a flat "base section" so the weight could stand up properly.
As for size, I have an example of a Wille Manson "Cave Painting" weight, made in a similar way, that is 12cm (almost 4.75 inch) wide, and it is definitely a paperweight. And there are several known examples of millefiori patterned Paul Ysart weights that have a diameter of 4.5 inch or greater - known as "super magnum" size.
I will move this over to Paperweights where some of our American friends might be able to throw some light on the matter.