I would call it a workaround vs. a solution*--but a clever workaround. 😁
When you get to double digits, you will have to make either another style or manually edit the indent.
*A solution would be for InDesign to honor the character style settings on the numbered lists.
Just for the laughs. After I found this solution. I was having trouble with the alignment of the numeral list. And I found an article from indesign secrets, from 2013 the mention this bug. Soo.. It is a feature... 🙂
Also in the article has a coment from somenone with the name of David Creamer... Is it you?
https://creativepro.com/formatting-tips-bullets-numbered-lists/
If so. Could you share the document that you created? It's not longer avaiable at you server.
https://www.ideastraining.com/PDFs/IDCS6_NumberedListExamples.zip