Yes, we’ve even seen them placed on bookshelves while maintaining a little breathing room on one side for the rear-facing port. Just try to leave a little room for air movement.
While there are several factors involved with creating a precise and stable image the one that works best is starting with the speakers pointing directly forward and the listener positioned in an equilateral triangle. Then, depending on how far the room boundaries are (3-4’ recommended for 1st reflection off from side walls) toe in ever so slightly until you hear a precise image. Unless otherwise stated we do not design for direct on axis listening and wouldn’t necessarily recommend pointing the speakers directly at the sweat spot.