Yeah those blades are just too far open. I have a cam at least one or two sizes bigger than that, and it idles down to 600 pretty easy.(4speed tho). Almost sounds like your TC is a little tight.
Make sure the Vacuum advance isnt interfering.
Not sure what you mean by those blades are just too far open.
Sorry for the ignorance.
Still trying to learn something new everyday.
47 years and still working on it....