An interesting and completely justified question!
First of all: Basically, all your basic assumptions are right. :-) The default values of 0.50 for each Icon's individual Dry/Wet-ratio at a global Dry/Wet Offset of 0% can be considered a meaningful starting.
But - even minor changes to the Main Microphones capsules characteristics will already ask for different ratios; adding a Secondary Microphone will increase the wet-level considerably; the simple fact that MIR allows for moving a signal farther away from the listener _without_ changing the level of the dry signal has no real equivalent anyway*). And what's more: MIR has no chance to know how "wet" the original input signal already is, thus it can't compensate for any "built-in" room information. (Mind you - we have not even started to talk about the needs and habits of different music genres when it comes to the apired "wetness" of a recording. ;-) ...)
In a nutshell: There are too many variables to be taken into account, and therefore the honest answer is that there is not _one_ "real" setting, simply because the whole MIR concept never was about a scientifically "correct" model of a hall. Despite all its hi-tech achievements , MIR first and formemost followed an aesthetical approach. All final decisions and adjustments for MIR Pro and its Venues were done by ear (... much like any good audio engineer would do in a real hall).
And if you allow for a personal sidenote: Even _if_ we could achieve that outmost realism, this would not mean much from a producer's point-of-view. Music production is hardly about "It has been like that" - it's much more about "This really sounds as it _could_ have been like that."
*) This "pop music mode" (as I like to call it) takes place as soon as the Distance Dependent Scaling is switched off in the Global Dry Volume Handling section of MIR Pro's Output Channel. BTW: Using MIR for acoustic pop music productions I tend to start with a -30% to - 35% Global Dry/Wet Offset. :-)
Kind regards,
