How can I call a smart contract from within another one?

The question is pretty straight-forward: How can I call a smart contract function from within the execution of another smart contract function?

The context for this question is an answer I got on my previous post, stating that there is a (pretty limiting in my opinion) cap of 20kb smart contract size.
For a possibly big project I need to separate different smart contract tasks into multiple contracts in order to stay below 20kb.

The DVM documentation mentions the SEND_DERO_TO_ADDRESS function which takes an address in raw and the amount to send.
Is there some special syntax to use it to call a specific smart contract function?

Is what I am trying to achieve currently impossible on DERO and if so, are there any plans to implement such a feature?

No, SC calls to another SC are not allowed on DERO network.