I recorded a large choir back in May with a pair of CM3s (NOS, on top of 10' light stand on top of about a 2' platform) , and it seemed to me that they were very pleasant and smoother sounding than whatever it was the church used for their own recording. I ended up using their video and my audio just because I liked the CM3 audio better.
I suspect I may have run into a negative aspect of gain from boundary mic recording by accident. I set my camcorder down on a sill in an about a 3x6 opening in the back wall of the church to record a joint elementary/teen choir last week when I had to run out to another meeting. When I first watched the video later, I thought, wow, those kids are really singing, and then I started hearing slight distortion in the recording. Puzzling since the camcorder was set on automatic gain. The kids weren't even mic'd. hmmm, I wonder if that opening acted like a funnel and the sill acted like a boundary which was too much for the internal mic on the camcorder?
So now that's at least one other person on TS that has these! Time for a Team Line Audio thread I guess.
That's exactly how I intend to use them myself (same height stand, same spacing). When using regular cardiods for choir, I would always go with DIN or ORTF if in a nice acoustic, but the CM3s seem to need a bit more spacing. I've spoken to people who have gotten good results with distances as small as 24cm for close-up recording. I won't get the chance to do large choirs until January, but will have a few small choir recordings in the next few months.
Regarding your camcorder, who knows what kind of wacko stuff the auto gain may be doing. My camera very obviously jacks the gain way up when it senses the average noise level dropping for any significant period. For the marching band show I just recorded, that meant anytime the band had a rest of more than a second or so, up the gain went and then unfortunately the wind and background noise along with it. Basically my camera audio is unusable for anything but dialogue, indoors, at steady level and close distance. And half the time that sounds like crap. This is a point-and-shoot camera though; not a dedicated camcorder.
Does your camcorder have a shotgun or other type of directional mic? Because then you could have been having proximity effect issues with it picking up the reflections off of close boundaries. Even if that wasn't happening, at the distance that the mic probably was from said boundaries, you could have been getting all kinds of comb filtering / phase cancellation. As described by Jon and Gutbucket earlier, a real boundary application means the capsule is very close to the boundary to both maximize the boundary effect and also avoid the comb filtering you get at intermediate distances. Combine that with auto gain and things could get pretty dicey.
Here's a very simplistic illustration: