I have had a lot of trouble with front STIs shifting properly. It just seems to be very sensitive to my crappy skills, as well as the exact, perfect, mounting of the derailleur, the model and more. I had a 105 setup, never could get it right, so I swapped FDs with what I had in the bin, a RX100 shifter, and it worked great. As luck would have it, the next bike I worked on was all RX100, had problems with the front shifter. So I went back to the bin, the only thing I had left was the 105 derailleur I pulled off the prior bike. You guessed it, the 105 derailleur worked great on that bike.