If you nest two large (or two small) that are consecutive in size, you will have 1/4 inch border.
If you nest a large and a small that are about the same size, you will have 1/8 inch border.
I don't quite understand the scallop question. If you put a large scallop with a large classic, you see only the scallops. I like to use a large scallop with a small classic and see more border.
I copied this from spellbinders website. Maybe it explains it better. http://spellbinderspaperarts.com/classic-circles.html
Classic Circles feature four sets of Circle Nestabilities®, including two straight-edge shapes, S4-114 Standard Circles LG and S4-116 Standard Circles SM. These two sets are also found in Nesties™-004. Also included are two classic scalloped-edge shapes, S4-124 Classic Scalloped Circles LG and S4-125 Classic Scalloped Circles SM.
Purchasing the Nesties™ Set saves 20% over buying each individually.
The difference between die template sizes within a Nestabilities® set is ½”, which becomes a ¼” border when layering. The difference between LG and SM Nestabilities® sets is ¼”. Combining both the LG and SM sets of Nestabilities® will allow for ⅛” borders when layering.
Here is the link to the ovals http://spellbinderspaperarts.com/classic-ovals.html