Another tricky thing: the QF, AA or CX may refuse you entry with a T5 boarding pass.
Lounges bill the entry fee to either the FFP or operating airline.
The operating airlines/FFP may refuse payment if the passenger accessed a lounge in a different terminal.
We have such a situation in MUC. TK flies from T1. The Lufthansa Lounges are in T2. These lounges turn away eligible pax, who are departing on TK.