Use top level OA & SF during allocation

I have a problem to manipulate top level OA (top level OA is an OA which contains other OA) and top level SF during the allocation.
In the example model from Capella (IFE system), there is diagram [SAB] Top Level system overview:
It is easy to allocate the SF “Watch video on Private Screen” to the actor Passenger : drag and drop; but I don’t find the way to allocate the
SF “Entertain with IFE System” to the passenger. How do you realize the diagram "[SAB] Top Level System ?
I have the same problem with OA.
thanks for your answers.

Hi Frederic, i think that i’ve already been confront to this problem .
I don’t know if i handle Capella correctly, but i remember that i can’t allocate a SF which contains other SF .
To realize this [SAB], the only solution i found was to drag & drop the “children SF” (Watch video on Private Screen, and the other) outside the “mother SF” (Entertain with IFE System).
Now you can allocate the SF “Entertain with IFE System”.
You just have to drag & drop again the children SF into the mother SF.
If someone know why it’s not possible to allocate a SF which contain other SF …
EDIT :In the SAB , allocate functions with the “Manage Function Allocation” ( in the Palette tool ) After, use the “Allocated Function” to display the mother function. It’s not possible to display it by drag & drop, but it work good with the “Allocated Function”

Thanks for this tip, it’s working.