High Casual, in my experience and during I short time using the term, has been nothing more than an advanced RP put into casual to avoid any potential advanced stigma. 

Most in HC could do advanced if, and when, they wanted even if there wasn't a 2-3 paragraph minimum. 

To me, it's usually a useless tag. But it has its use, casual draws a lot more people, so HC satisfies a variety of needs. Not enough to warrant its own section, however.