A difficult prospect. Unfortunately the last trial was relatively ineffective at both lower doses and only the highest dose showed a promising data point. It's been a while since I had a math class but, from what I remember it's a lot easier to plot an accurate graph with more than a single data point. ;-)
I believe that is the intent of the 400 mg arm. If previous results carry over 300 and 400 will make it possible to draw an accurate graph. I believe they are trying to find the best balance of safety and effectiveness along the plot line. I'm anticipating between 225 and 325 to be the sweet spot.
The preclinicals predicted a dose dependent response to the best of my recollection.