Bigger midranges/speakers have better imaging?

One of the easiest imaging "special effects" is to up-fire coherent speakers: soundstage floats mid-air high above and well beyond the speakers. Not traditional "pin-point" imaging but palpably sized phantom soloists etc. to relax to.
Anyway, it's a rare example of visualizing the position and size of instruments on stage. It's artificial, but it still allows to 'measure' the soundstage (or speakers imaging) in a way.
An even better 'instrument' to 'measure' imaging & soundstage is to arrange an acoustically transparent curtain [*] so you can't see your speakers and their arrangement. Conduct DBLTs and make notes of what you hear before you know what you are listening to.

[*] eg speaker grille cloth from a reputable speaker maker