When this question came in I tried to use my high school geometry. Then when my brain started smoking my buddy Adam took the question and went over to the guys at LumberJocks.
Attached is a photo of a sculpture I made with the kind of base I’m making with the compound miter. Once I figure how many degrees I want for the outside slope is there a scale to predict the miter angle?
Here are images of his sculptures:
Check out this LumberJocks thread for the ratio!