Originally Posted by froinlaven
It's just basic math.
The left and mid are the same track. The right side is inverted.
If you are adding gain to the mid, you are also removing gain from the right while also adding gain to the left.
It pays to actually understand what one is trying to do when one experiments. That said, an 'unexpected' result such as this one is a message that should tell the experimenter: something is wrong with your precepts -- go back to square one and figure out where your understanding went wrong. (And, hey, it takes more than a minute for most of us to wrap our pretty little heads around M/S mic technique and M/S mix affects.)
It's hard not to be sympathetic with newbs here -- since there are a number of people here talking with much certainty but with precious little actual solid knowledge who mangle and confuse the 'facts' and trumpet them across the BB.
GS can be a great resource -- there are some deeply knowledgeable and experienced people here -- but there are a large number of people here who have little technical understanding but act as though they know everything there is to know.
If you don't already have a pretty good knowledge base, I strongly suspect it can be a real headache trying to figure out who is credible, who is full of nonsense, and who floats in between. (Full disclosure: I count myself in the floats in between