Cathe, I've been thinking about this for a long time (or at least when I saw your beautiful work) and now that I’m starting to work with circles (curves) I think I’ll think some more. Maybe in the future…
I found this site with directions, are they close to what you used? It keeps redirecting me to another page, but should work:
http://www.geocities.com/Heartland/Acres/6349/PatBlueDahlia.html
I also saw this site with a mini Dahlia and liked the results too:
http://www.minisbycarol.com/dahlia.htm