As far as marketing goes, certain genres 'outweigh' others. The Lovely Bones, to take your example, is TECHNICALLY a fantasy novel. But since it goes to the literature section, it is in the literary genre. Another example is Kurt Vonnegut. Almost all his books are 100 % science fiction, yet you will never find them in the SF/F section. They are always shelved as 'literary.' Likewise, the 'horror' designation will outweigh the 'fantasy' designation--many horror novels are fantasies as well--horror also outweighs literary, science fiction, and sometimes mystery. Sci fi or fantasy usually outweighs mystery. On the other hand, lots of pop literary bestsellers incorporate many science fiction elements.
To take another example, Haruki Murakami always appears in the lit section, but his stories are MUCH more fantastic than most fantasy I have read.
It all has to do with what the publishers think shoppers in the different sections will be willing to buy. It will be tough to sell a book with a dragon on the cover in the lit section OR the mystery section. But in the sf/f section, the book with a dragon on the cover is purchased happily.
I'm not trying to put down any genres at all. My favorite genre is sci-fi, and there is a lot of back-and-forth in the sci-fi community about whether SF is a "ghetto" that books get placed in if they don't merit the designation of literary. I'm not trying to comment on that issue here. I think a given book has to be compared to others in its various genres to see where it fits the best. Diane Gabaldon writes books that are both fantasy and romance, but they end up in the romance section usually.
What genre do your books fall into? Maybe we can brainstorm some others in a similar cross-genre situation to help you sort out which is the main genre!