your question is interesting.
For C style language the more function
(mean the more code) get more data to use.For example

func1()
{
char a;
int b;
}

.
.
.

func n()
{
char c;
long d;
}

For assembly style I get neccesary variable on RAM only (ie need to memorize or be status) other calculation is implemented on register bank then it will use less RAM.

However C linker have directive OVERLAY
which will utilize usage of RAM.
The linker will be create call tree of whole software and examine the same level of branch.This mean that while one function is called. Other on same branch won t be called until it is finished.

The RAM which is reserved by first function on a branch will be reusable to other branch if you declare as dynamic one.

For this OVERLAY the RAM growth will be less upon ROM and more depend on level of call tree (hiearical level).

Best Regards