Any reason why you couldn’t just put that speaker in the bookshelf? Locating the rears far-to-the-sides is your best option, IMO, so you really should try to figure out a way to make it work. Your other positions are going to put you dealing with the near-field “hot spot” problem that has been mentioned.
Speakers placed up high should be inverted for the same reasons floor speakers are positioned up-right: It puts the tweeter closer to ear level, and further from boundaries, while the woofer is closer to boundaries, which enhances bass output.
That said, if you’re stuck with the “near field” placement I’d go ahead and put them in the traditional orientation. That will put the tweeter further from ear-level, which will help “de-localize” the speakers.
BTW, I’ve had to deal with too-close surrounds before, so I can give some tips on dealing with the localization problem, if you end up going that route.
Regards,
Wayne A. Pflughaupt