("As the source is brought closer to the directional microphone, the amplitude component of the pressure difference increases and becomes the dominant component at lower frequencies.") It's not like there are some weird kind of reflections going on that only occur when the mic is physically close to the recorded object causing the effect. It would definitely be a great thing to test in a controlled environment... or I could be reading this stuff wrong, it's not the clearest!
Yeah, I seem to remember reading that myself, both the wiki and the shure bits. Re-reading, it seems like maybe you're right. Huh.