Because you need to know the spring angle of the size crown you are using, it's hard to get exact settings for a coumpound cut.
Unless you are using a really large moulding, just turn the moulding upsidedown,and place it on the saw table as it would sit on the wall,and make your cuts at 45 deg.
If you want to see something really funny,ask the person at H.D. or Lowes, what the spring angle of the crown you are buying is.Luck