Sagan out of necessity and perhaps preference freelances more than any successful sprinter I can remember. He is rarely the recipient of a classic lead out train. He is also very willing and able to adjust and change wheels as the sprint is winding up, and tends to pick the right wheels. As a result he is almost always close at the line. But he is often giving up ground to riders of equal speed somewhere in the sprint that he has to make up.
Agree that Cav seems to be over reacting to any hint of contact.