Configuring the symbols allowed by different model types?

Hello all.

I've just created a new symbol in ARIS symbol editor. I've added it in ARIS IT architect by clicking on a random symbol I don't really need in a method, and clicking New (I haven't found a way to just add a new symbol without using an original symbol?).

I've found that one of the model types I have, Process Context Diagram, doesn't seem to allow this symbol to be added.

How do I get around this?

Thanks.