It's no for some outliers but for the rest of us, yeah, taking up shelf space isn't enough or isn't quick enough. If you want to achieve audience awareness, I don't think passive works anymore and you'll have to have some kind of marketing campaign.
I have a pal who is on this aspect all the time. She does freebies on Select and then promos them everywhere. She does quite well sales-wise. Not up at the top of the charts but steady sales.
I don't know if FB and Twitter work. I'm sure they do for some but perhaps you need a fanbase first. Personally I'm sick of seeing someone flogging their books everywhere on FB and having every instance of it wind up on my wall. I've unfriended some individuals for such egregious behavior which is the opposite of what they want.
So you need to keep the annoyance factor down.
Anthologies. I'm not sure why these took off but apparently readers see it as a good deal.
Right now (the price will go up by the first of the year) the Flash anthology is basically $1 a book. So that is a good deal. You could price a 3-book boxed set for 99 cents and that would be a fantastic bargain.
But people still need to know it exists. You can't rely on them finding it among the millions of books now on Amazon. You need to find a way to point to it.
I've approached book bloggers in the past months and they were unaware of my books and very enthusiastic to read them. That made me realize there are just too many books out there to expect to be easily found anymore.