FGT Session-Helper, how to use the same port for different session helpers?

How does FGT support same port but different session-helpers ? With checkpoint you can define a service and apply a session-helper multiple times, and then apply to the policy. So you can exlude ftp handling from most, as it only applies if policy matches. Don't know if you can do that in FGT. And you can have the same port with multiple protocols and the policy decides which session helper to use. How does that work on FGT?