Nice discussion, but one thing has not been mentioned: perhaps the mastering engineer that started all this has a very particual view on how much stereo signal there ‘should’ be in a mix. Personally I don’t believe in such rules, and if a mix sounds good when nearly mono, then it IS a good mix. Remember, some of the best classic albums (Pet Sounds, Sgt. Pepper’s etc.) were originally mixed in mono - even relatively modern ones (Pepper’s Californication is almost mono), so no shame in that!
well, if you use LCR panning style, there will be side information.
just imagine a saw wave panned hard-left, and no signal on the very right. S = -L + R. so by flipping the polarity of your saw and adding R (which equals to nothing), you get… your saw wave with a flipped polarity. eg. you have Side information. and indeed, it makes sense that if something is panned, there is stereo. dead mono means that subtracting L and an inverted R entirely cancels out the signal. so there is some misunderstanding going on somewhere ‘in the chain’ between the ME and you.
Good point. Really good point, actually.
Care to hear my mix?
PM me your email and I will send you a song for you to listen.
(btw. this is horses for courses, but very broadly speaking, when mastering, i find an RMS ratio of Mid vs Side where the Side is about half as loud [RMS] compared to the Mids is quite pleasing. eg. if the Mids alone were hitting an RMS of -8, the Sides around -14 are very generally in the ballpark, for me anyway. but some vintage sounding mixes can be very mono and sound cool. and then some modern stuff can get super-wide in choruses, mono compatibility seems to matter less and less.)
Hi Denicio - how did your Mid/Side balance sound compared to the references you had in mind when creating your project?
(Or … maybe your engineer had his mono button pressed by mistake! 
).
Alexis,
Well I quit comparing my mixes to commercial mixes years ago. Personal choice really. It always had me chasing my tail. SO I rarely (like never) have CD’s in my player when mixing.
is this wise? Dunno, probably not. Just never found a benefit to A/Bing while I am working.
D