Eladan:
I went down this rabbit hole myself. You can read my initial thoughts here: https://www.rolemasterblog.com/spell-law-deconstruction-written-magic/
Some other questions or comments:
1. Where do the creatures come from that are summoned? Are they magical constructs or are they drawn/teleported from nearby?
2. Once a circle is drawn/written can it be re-used repeatedly. For instance, a circle chiseled into a stone floor?
3. Drawing time. Given that a circumference is roughly 6x radius, drawing time is a function of circum AND the medium? Chiseling is slower than painting, painting is slower than drawing in sand etc.
4. Should the medium of the drawing reflect not only its susceptibility to damage but also it's power level? Or should it be reflected in casting success?
5. If a creature is summoned into circle, do they need to return to the circle to be returned from whence they came?
6. The circle needs to be large enough for the specific creature to fit into.
