The whole idea of using shotgun microphones for stereo music recording is a shaky proposal from the start. They aren't "audio telescopes" the way people seem to imagine, and they aren't very good general-purpose microphones--they are mainly designed for speech pickup. Their special directional effect is only at speech frequencies, specifically in the range where consonant articulation occurs. Their directionality is no greater than that of normal directional microphones such as supercardioids until you get up into the kHz region.
Also, their off-axis response at high frequencies tends to be quite uneven. The manufacturers of low-cost microphones don't generally give polar response diagrams at different audio frequencies, but that's where this shows up. Even at normal pickup distances for live performance music recording (out in the audience), a lot of the musical sound that you pick up is off-axis because it's been reflected from various room surfaces. Most people underestimate the percentage of reflected sound in their recordings but if you can imagine how things would sound in an anechoic chamber (like outdoors acoustics only more so, very creepy) you might begin to realize it.
Anyway, to put it bluntly, the off-axis response of all but the very best shotguns--only three or four multi-thousand-dollar models--positively SUCKS at high frequencies: muffled AND spitty at the same time. And those three or four tolerable-sounding ones for music, by the way, are all short shotguns, so the effect they have of seeming to bring the sound source closer is not as great as you might hope.
Sorry to seem like such a downer here but ever since I got to this place I noticed that there's a huge amount of swallowing of myths here on this topic. People who work professionally with shotgun mikes--film and video sound recordists--would never think of using a pair of them to record a concert (although M/S with a shotgun mike for M isn't out of the question) and mainly, would never think of using them at the distances people here typically use them at. The whole point of an interference tube is to create shadows in the high frequency response for off-axis sound. When you're so far away that most of your sound is coming at the mike from off-axis, that's just not the type of microphone to use.
--best regards