When you have two microphones in the player position, there is a stereo image of horizontal spatiality. However, with the delay effect, you have a depth perception because as the grand piano is extensive, the resonance produced at the end of the harmonic board takes a few milliseconds to reach the player's ear. Using the delay effect, this depth can be felt using only two speakers in front.
My favorite preset is Steinway D Player Wide. In my opinion, after many tests, this best simulates this depth effect, as it uses 5 microphones strategically positioned around the entire piano, covering the entire dimensionality of the instrument. But this dimensionality can only be felt due to the delay effect on each of the microphones and the master effect. Otherwise, the frequencies would come together in the speakers and there would be phase cancellations or, at best, a merely horizontal perception of sound, without depth.
Respeito, Esforço e Sabedoria