My 2015 Defy had an Ultegra 6800 SS (short cage) and handled an 11-32 with no problem at all even though the published max spec. is 28t. The corporate Giant store setup it up that way for me when I bought it and I never had an issue at all. It always shifted well. Shimano is notoriously conservative.
My new bike that I just picked up last week came with an 11-34 and I am going to swap that out for an 11-32 which just arrived today. I don't like the 11-13-15-17 gearing on the 11-34 and much prefer the 11-12-13-14 on the 11-32. I'll keep the chain the same length and will be able switch back to the 11-34 if the need arises.