Learn English – the term used to describe when two different things both rely on each other

That's actually a very uncommon thing in the U.S. because of employment law. Calculating overtime in those situations is difficult and having a policy like that can put employers into bad legal situations.

To further complicate things, each state has different rules, there is no common terminology, and in fact sometimes it's addressed by case-law rather than actually being addressed by written employment law.

Terms that you might try looking up are "scaled", "blended", "differential", "weighted" associated with "pay", "payscale", "rate", or "wage".

This isn't a topic that's easily googled. You'll want to go directly to accounting or HR online communities.

'Oxymoron' is probably the word you want.

a combination of words that have opposite or very different meanings

[Merriam-Webster]