[thewas] It isn't as we don't listen usually in anechoic chambers so we hear also what happens at the other surfaces from room reflections.
[garyrc] While anechoic chambers may help in design, we listen in neither anechoic chambers nor with our ears on top of the speaker. We hear speakers in listening rooms, and moving a single microphone several inches in a room can produce appreciable differences in the measurements. I would think we should measure with several mic positions with some way to combine the measures meaningfully (as room correction equipment does), or, for solo listeners, use three mic positions: left ear, right ear, and, just for fun, nose.