chikkenguy, a 110-degree angle for two near-coincident cardioids normally gives a solid stereo image across a nice, wide stereo pickup angle. With 17 cm spacing between the capsules, that's well known as the "ORTF" stereo pickup method, and I'd guess that this is what your book was talking about. But given the narrower pattern of supercardioids, the angle between microphones needs to be narrower as well.
The Schoeps MK 41 is actually somewhere between a super- and a hypercardioid, so this difference is really significant. With the setup you described, you were "starving" the center of the stereo image and you also were most likely aiming the null of both capsules at some part of the direct sound source. That's generally not a good thing to do with any directional microphone.
In general, the closer a microphone's pattern is to a figure-8 (pure pressure gradient), the more nearly that microphone's off-axis response will sound like its on-axis response--though of course the off-axis response will be weaker because of the directional pattern itself.
In case that was obscure, let me say it another way. With a good figure-8 microphone, the frequency response can be essentially the same at all angles, except for right around the null at 90 degrees; the sensitivity, however, will vary greatly at different angles of sound incidence. Meanwhile the opposite behavior occurs at the opposite end of the pattern spectrum, with single-diaphragm omnidirectional microphones (pressure transducers): Their sensitivity (say, at 1 kHz) will be the same at all angles of incidence, but if the microphone is of the normal size as used in studios, its on-axis response will be quite different from its off-axis response in some range of high frequencies.
Since the Schoeps MK 41 is closer to a figure-8 than a cardioid is (i.e. it has a greater proportion of pressure gradient response as opposed to pressure response), the off-axis response of the capsule is closer to flat than that of a comparable cardioid such as the MK 4. Does that make sense, I hope?
--best regards