Orion seems to start with suggestions as you expect on the fourth character. Try it with "amaz" instead of "ama". That said, I would greatly prefer local (bookmarks/favourites/history) suggestions from the first character. In other browsers, I usually enter a single character as a fast way to reach a certain subset of my bookmarks.
(edit: though it only shows them in a list below the input on the fourth char, not as a completion in the url-bar.)