I've met that request on another site too, especially from HTPC users. I sadly did not think about that when writing the app, I just wanted to keep things simple by limiting the number of parameters. Now I've already moved on to other projects, so the tweaker is not under development anymore. There's already a mod offering an intermediate P-state, but only in the GUI and not in the service if I remember correctly (haven't tried it myself). Links may be found here.