Don't forget toe-in, which can not only affect imaging but widen the sweet spot. Some speakers sound better below the tweeter axis, and with little to no toe-in.
For me, that vast majority of speakers I've had "disappear" better when I don't toe them in much - i.e. closer to angled straight ahead. Toe in tends to bring in more image precision, but also tends to tighten up and squeeze the imaging and soundtaging. Toeing back out loosens things up, expands the soundstage and imaging, and seems to free it more from the speaker. Sort of like the difference a lot of people hear between a classic solid state amp (heavy toe in) and a classic tube amp (toe out).