Feierabend's projected improvement is actually pretty aggressive relative to others - check out other similar-aged pitchers like Gio Gonzalez or Yovani Gallardo. So I'm not sure how to respond to that case. I did find a relationship between batted ball rates and changes in strikeout rates in young pitchers, and Feierabend profiles well in this sense. Along with better results on balls in play and an improved walk rate, he's projected to shave off half a run from his ERA over two years. That's actually a very good rate - most pitchers don't improve that rapidly during their fifth through seventh years of professional baseball.

Lowe's projected growth is pretty typical for a pitcher entering his mid-20's - very little improvement. Remember, strikeout rates are already declining for many pitchers at this stage of their career, so it's difficult to project great leaps of development at this stage of a career. Lowe might be a special case due his role change and elbow issues, but we don't have a good way to account for that. His overall projection is low because, well, he wasn't very good before 2006.

David Gassko might be a better person to ask about the Clement vs. Jones projections because he handled a lot of the work involved in generating the baseline projections... which is what your question seems to be targeting. Jones is projected to improve much more over the next few years for a number of reasons, but Clement is projected to be the better hitter right now. Because there's so little performance data available for Clement, it probably has something to do with the way we accounted for his 'player type' while regressing.