Originally Posted by cyccommute

While front derailers are sized for a range of outer chainring diameters, the range is very broad. I've used Ultegra for 52/40/30 and 50/39/24 triples and have used Tiagra for 50/39/28 and 46/34/20 without issues. They all shift just fine.

Shimano's tech bulletin on the Ultegra 6703 derailer says that the minimum difference between the outer and middle ring is 13 teeth which puts your combination well within the range. Something else must be off for the derailer to hit the middle ring. The alignment may be off.

On a side note, I've never found STI to be that fiddly to set up and use. The Tiagra front derailer is actually a better derailer for triples than the Ultegra, however. It's easier to set up, is more forgiving, and can be used over a wider gear range than its more expensive brothers.