Referencing earlier passages: Cross reference or "as discussed earlier"
What you prefer is barely relevant; think of the reader. It so happens that earlier today I was consulting a book to find a specific method. I quickly found an example of its use, but the book said '...as explained in detail in Chapter 13...'. Chapter 13 was a long chapter. The explanation when I found it was very short - and it took me a long time to find it.

In general, the more cross-references the better but you have to credit the reader with some short-term memory. A cross-reference to the previous paragraph would be more irritating than helpful.