Getting back on topic, another thought about the epic scale that may be relevant;
Epic scale stories tend to have a lot of things going on in them. There are pacing concerns involved with this.
Suppose you have eight or nine major plot strands. If you are going to give each of them equal time, it means that in a hundred-thousand-word volume (which is about as big as individual volumes get these days outside of exceptional circumstances, and most of us aren't Susannah Clarke) each of them will only get a bit over ten thousand words. So one failure mode here is it feeling like the book is going on and on and on with not enough to be interesting happening in any one thread. (Another failure mode is some threads just being dull and people being annoyed every time they show up, but that;s not one that structure hacking fixes.) Examples of such in the epic-fantasy mode are left as a fairly easy exercise for the reader.
The other option there is for each significant chunk, volume, call it what you will, to focus primarily on one or a few threads and background or leave out the others. Do this wrong and readers get bored and miss characters they care about, or worst-case have forgotten what they're meant to care about when they get back to it. Do it right and you can use it to build tension. If Sarah and John separate to go on different missions and your readers will be stuck with Sarah for the next hundred pages, her worrying about John every now and again or being reminded of him by something happening he would have appreciated being there for can help keep John in the readers' mind.
An example I would suggest of doing this right is Dead Beat. Dead Beat mostly has its own necromancers-gone-wild plot, and some other story arcs like Mavra feed into it directly. But there's also an appearance by Johnny Marcone, which fits in with the book-scale plot though it's not a major element of it, but also serves to advance things with Marcone and Gard and give us a somewhat more overt clue than we have seen before about Gard being an actual Valkyrie, and sets up Marcone owing fro having interfered with where Harry was supposed to die; and Mab's appearance when Harry is expecting Lea advances the whole "something rotten in the state of Faerie" series-scale plot thread quite a bit in ways thatdo not directly connect to the book-scale plot, but that keep us as readers aware that this is still happening and still important. Jim is really good at weaving these things in to books that are mostly about something else.
