My standard test for speaker imaging is to play a true binaural recording made with a dummy head. If a pair of speakers can match the all around the listener directionality as the same recording played via headphones, then the speakers image well, and there is relatively little of the room contributing to the image. Horns tend to be better at this than cone 'n dome speakers because of the higher ratio of direct to room sound, especially if toed in. Dipoles tend to be predominately 'envelopment' from the room; I've never heard a dipole which can image to the side, above or behind the listener and they have a hard time with imaging outside the left / right boundaries of the speakers.
If speakers of any type are up against the front wall verses relatively far out into the room, it is very difficult to achieve good depth imaging behind the plane of the speakers, and envelopment. Horns out into the room (about 1/4 to 1/3 the room depth out from the front wall) can have the best of both worlds if done right.