Hector Santiago is nipping on the heels of Anibal Sanchez when it comes to Homeruns allowed per 9 innings. Sanchez sits at 2.22 while Santiago is at a career high 2.04 (for comparison, Jered Weaver is 1.85 and Jake Arrieta is .36). In fact, since Santiago's first full season, he has been trending upward.
2013 = 1.03
2014 = 1.06
2015 = 1.44 (what happened??)
2016 = 2.04
Some things that changed in 2015 is Santiago started throwing a slider (thanks Mike Butcher?), and he threw his sinker and screwball almost not at all (though to be fair those were rare pitches for him - he threw 125 of them in 2013 and 39 in 2014).