If you are going to use a bookshelf as a center channel, it should not be placed sideways. Typically speakers are designed for optimal horizontal dispersion, where people at the right or left of the listening area get as good listening experience as those in the sweet spot. If the speaker is placed sideway, the dispersion gets shifted to the vertical plane which is not what you want. Even more so for Klipsch with their horn wave guide that further minimizes vertical dispersion and accentuates horizontal dispersion, which would exacerbate the problem if sideways. Best to get a dedicated center ch speaker.