Topic = XY hypercardioids.
I don't speak Schoeps, but I gather the MK4's are hypercardioids?
If so, then our experience MANY years ago recording the Grateful Dead plays in here. We wanted to do AUD recordings from FOH, about 40-50 feet from stage and asked our mentor,,,,, a studio engineer, former FOH guy. He said Hyperss in XY will reduce some rear crowd noise, add some center balance and that is what we used for almost 100 shows. (Beyer M201) Many heads were enamored of the sound of these recordings, some would ask, "is this a soundboard"? especially the ones where we were about 40 feet from the stacks, DFC. Years later, a taping buddy had moved to Denver, made friends with Mark Nutter and started seriously buying microphones etc. He calls me one night and says, "hey, you know those XY recordings we made all those years ago don't have very much stereo separation?" So I Say, This is/was true, but can you recall ever listening to one and thinking it sounded "wrong"? No, because that up front XY hyper sound on the recordings of the Ultrasound PA was so righteous.
XY CAN be useful in certain situations, don't let a book tell you otherwise.
e.g.:
https://archive.org/details/gd1983-05-14.141945.beyerm201.executivecrew-holbrook.flac2448