I am having a similar problem as Marcelo...
However, in order to keep the agenda flat I only want the parent PROJECT
headline (the inner most) to be the prefix.
In his example this would be the following:

My-sub-sub-project *NEXT Call Liz RE: account creation             *
:@call:@work:

The problem is that I did not yet find out how I can get the <*parent
project headline*> (in this case: *my-sub-sub-project*) as *agenda prefix*.

Until this is solved I rewrite the project name for all todo-headlines in
the project.

Greetings,
Eraldo