Are you making shells all day or only in the evening ? Have you ever done traditional prep? It might give you a little more bang for your buck. If you haven't, you should try it for a while to find out how many tablespoons you find to be reasonably satisfying for one whole session.
1/2 pound in two days is a lot, but I suppose it's not completely unheard of if you're a hard head, especially if it's weak kava and you're always in search of the 'full' experience.