How is RX revenue determined?

Hi, am a college student and I've been trying to learn more about RX - one question that I wasn't able to get a clear answer about was how the cash to advisors from an RX engagement is earned. 

I understand that it is not as consistent as the case for M&A and cap markets engagements (which are typically % of consideration), and there are different norms depending on multiple factors e.g. debtor/creditor side, complexity, engagement duration, collection %, etc.

Don't really have access to anyone in the field right now and to my knowledge only in-court restructurings/liquidations disclose precise fees (which I am unable recognise a pattern for)

Would love if any experienced professional could provide more colour on this TIA!