If I were being more scientific, I’d have done each of these steps individually and made an experimental cut, but I’m impatient, so I plunged ahead with all of the above suggestions:
- I ran an update on my system, presumably catching Inkscape if it needed it.
- I resized the document to 20"x12"
- I verified that Inkscape was using 96 pixels per inch (which it defaults to, but there is a setting)
- I shrunk my stroke width to the absurdly small 0.001mm, which means that I couldn’t see the strokes anymore, but View/Display/Outline helped make the lines visible at the expense of no longer seeing the elvish runes.
- I set the W and H for the inner circle to 40.5mm, and then used Align and Distribute to center the two cut circles and the engrave image.
- I pressed The One Button, and things turned out great.
Thanks for the tips! I don’t know which one or ones made the difference, but I’ll definitely try to use small stroke widths if I care about the size I end up with.