Requirements Engineering Methoden

Jeff Patton wrote an article about goal levels, that I described in my earlier article Abstraktionsgrad von Anforderungen. He refers to Alistair Cockburn for the description of levels.

What I find an interesting point in Jeff's article is that the same requirement may be on different levels, depending on the context.
He finds two examples, where buying coffee can be either on fish level when I'm ordering a breakfast - or on sea level when I need to get coffee. The other example is looking up an email address for a friend who asks for the address of another friend (sea level) or looking up the same address while sending an email message (fish level).

When designing an email client, you would have to figure out which of the two scenarios is the more likely one. For this one you should write the use case.
It does not make sense to repeat the same use case from the sea level on fish level, obviously.
Still the fish level use case should be a considered scenario when designing the software - otherwise you would lose the possibility to look up an email address without having to write an email message...
I guess, I would try to cope with this in the use case's trigger. Other ideas?